Gene Likens - Academia.edu (original) (raw)

Papers by Gene Likens

Verhandlungen, Dec 1, 1990

The Hubbard Brook Ecosystem Study (HBES), begun in 1963, is an ongoing , longterm effort to under... more The Hubbard Brook Ecosystem Study (HBES), begun in 1963, is an ongoing , longterm effort to understand the structure and function of forest watersheds and associated aquatic ecosystems at the Hubbard Brook Experimental Forest in New Hampshire. Chemical analyses of streamwater and precipitation collections began in 1963, and analyses of lakewater collections began in 1967. This publication documents these collection methods, sites, and analytical techniques, providing a complete record to ensure the integrity of HBES data. The evolution of the HBES chemical data management system and the development of quality assurance procedures are described, as is the general algorithm by which ecosystem chemical inputs and outputs are calculated. These data represent a unique and important contribution to ecosystem science and provide an internationally recognized benchmark for assessing ecological changes.

Journal of Environmental Quality, May 1, 2000

The geographical and chemical origin of SO4deposition has become a concern, because anthropogeulc... more The geographical and chemical origin of SO4deposition has become a concern, because anthropogeulc S emissions have influenced the biogeochemistry of forested ecosystems and surface waters. Our aim was to evaluate the origin of SO~-in bulk precipitation at the Hubbard Brook Experimental Forest (HBEF), New Hampshire. We analyzed 26 years of archived bulk precipitation samples for sulfur stable isotopes. We compared the ~4S values with anthropogenic SOs emissions, the relative contribution of sea salt aerosols (as the SO42-fNa + ratio in precipitation), and temperature and solar radiation effects on the long-term patterns of fi34S values. The long-term pattern of ~4S values in bulk precipitation could be explained partly by the relative contribution of marine O−˜orsolarradiationbutnotbytemperaturevariationoranthropogenicSOsemissions.Thehighvariabilityofthefi4˜SvaluesofvariousfossilfuelsmakesitdifficulttousestableO~-or solar radiation but not by temperature variation or anthropogenic SOs emissions. The high variability of the fi~4S values of various fossil fuels makes it difficult to use stable O−˜​orsolarradiationbutnotbytemperaturevariationoranthropogenicSOsemissions.Thehighvariabilityofthefi4˜Svaluesofvariousfossilfuelsmakesitdifficulttousestable isotopes for identifying whether changing fossil fuel use is affecting the ~4S values in bulk precipitation. The seasonal pattern of fi34S values in bulk precipitation (significantly higher values in the winter than the summer) may be explained by the temperature dependence of the isotopic shift during SO42-formation in the atmosphere. A greater relative contribution of marine SO~ during the winter also may have contributed to the higher ~4S values in the winter. Previous investigations may have overestimated the role of biogenic emissions in affecting the fi34S pattern. I NOUSXR~AL~ZED regions of the world have been confronted with the consequences of acidic deposition since the beginning of the twentieth century. High SOl-deposition has resulted in SOl-accumulation in forest soils and acidification of surface waters. Despite the fact that SOl-deposition and SOl-concentrations in soil solutions and stream waters have been reduced considerably in northwestern Europe and eastern North

The Ithaca MAP3S Regional Precipitation Chemistry Site, in continuous operation since September 1... more The Ithaca MAP3S Regional Precipitation Chemistry Site, in continuous operation since September 1976 is now operating on a daily sampling rather than event sampling basis. Two other network stations (NDDN and EFPVMN) are co-located currently at the site. Research associated with MAP3S over the last year includes an analysis of the impact of changing emissions levels on precipitation chemistry in the eastern US. From 1977 to 1986 a 20% change in SOâ emissions and a 10% change in NO/sub x/ emissions have occurred over the eastern and midwestern US. Six continental precipitation chemistry sites from the MAP3S network, plus the Hubbard Brook Experimental Forest, New Hampshire, show a direct relationship between emission levels and precipitation concentrations, except for Penn State, Pennsylvania. MAP3S sites at Illinois and Ohio, located closest to the major SOâ source regions, demonstrate statistically significant (P < 0.05) linear regressions of SOâ concentrations on SOâ emissions. Hubbard Brook shows the strongest relationship (P < 0.01) between SOâ emissions and SOâ concentration in precipitation. Only Whiteface Mountain, New York, shows a significant relationships (P < 0.10) for NO/sub x/ emissions and NOâ/sup /minus// concentrations. However, Illinois, Ohio, Ithaca, and Hubbard Brook show significant linear regressions of H/sup +/ concentrations on emissions of SOâ + NO/sub x/ (P < 0.10, 0.05, 0.05, and 0.01, respectively). Overall, for the entire region examined, decreasing SOâ emission levels appear to have decreased SOâ concentrations with an efficiency of 66% + 17% (s.e.).

Ecology, Aug 1, 2017

The Hubbard Brook Ecosystem Study officially began on 1 June 1963. This archive contains the resu... more The Hubbard Brook Ecosystem Study officially began on 1 June 1963. This archive contains the results of 50 yr of collection and analysis of (at least) weekly stream water and precipitation samples obtained during the period 1963-2014 (from 1 June 1963 to 30 May 2013). Stream chemistry for the nine gauged watersheds and precipitation chemistry for precipitation gauges distributed throughout the Hubbard Brook Experimental Forest are reported as concentrations in (mg/L).

Science, Jun 14, 1974

At present, acid rain or snow is falling on most of the northeastern United States. The annual ac... more At present, acid rain or snow is falling on most of the northeastern United States. The annual acidity value averages about pH 4, but values between pH 2.1 and 5 have been recorded for individual storms. The acidity of precipitation in this region apparently increased about 20 years ago, and the increase may have been associated with the augmented use of natural gas and with the installation of particle-removal devices in tall smokestacks. Only some of the ecological and economic effects of this widespread introduction of strong acids into natural systems are known at present, but clearly they must be considered in proposals for new energy sources and in the development of air quality emission standards.

University of California Press eBooks, Nov 25, 2009

Water Resources Research, Dec 1, 1974

Analysis of recent precipitation samples from the northeastern United States has shown a consiste... more Analysis of recent precipitation samples from the northeastern United States has shown a consistent pH of less than 4.4, when the expected pH based upon equilibrium with CO2 would be 5.6. A stoichiometric formation process being assumed, some 65% of the acidity is due to H2SO4, 30% to HNO3, and less than 5% to HCl. The pH values may be predicted from chemical content and generally agree to within 0.1 pH unit with the observed pH. The distribution of acid precipitation encompasses most of the northeastern United States. This pattern apparently has existed since about 1950–1955, but the intensity of acid deposition, especially that due to HNO3, has increased since then. Analysis of prevailing winds indicates that much of the acidity originates as a general source over industrial areas in the Midwest.

Hydrological Processes, Jun 28, 2017

We introduce a new representation of coupled solute and water age dynamics at the catchment scale... more We introduce a new representation of coupled solute and water age dynamics at the catchment scale, which shows how the contributions of young runoff waters can be directly referenced to observed water quality patterns. The methodology stems from recent trends in hydrologic transport that acknowledge the dynamic nature of streamflow age and explores the use of water age fractions as an alternative to the mean age. The approach uses a travel time-based transport model to compute the fractions of streamflow that are younger than some thresholds (e.g., younger than a few weeks) and compares them to observed solute concentration patterns. The method is here validated with data from the Hubbard Brook Experimental Forest during spring 2008, where we show that the presence of water younger than roughly 2 weeks, tracked using a hydrologic transport model and deuterium measurements, mimics the variation in dissolved silicon concentrations. Our approach suggests that an age-discharge relationship can be coupled to classic concentration-discharge relationship, to identify the links between transport timescales and solute concentration. Our results highlight that the younger streamflow components can be crucial for determining water quality variations and for characterizing the dominant hydrologic transport dynamics.

Marine Ecology Progress Series, Mar 15, 2006

Heterocystous, planktonic cyanobacteria capable of fixing atmospheric N 2 into available nitrogen... more Heterocystous, planktonic cyanobacteria capable of fixing atmospheric N 2 into available nitrogen (N) are common and critically important to nutrient cycling in many lakes, yet they are rarely observed in estuaries at salinities >10 ppt, even when strongly N limited. In a series of mesocosm experiments using water from Narragansett Bay (Rhode Island), we manipulated top-down (grazing) and bottom-up (nutrient) factors hypothesized to exclude heterocystous cyanobacteria from estuaries. We previously reported that planktonic, heterocystous cyanobacteria grew and fixed N in the absence of grazers. Here, we focus on responses to phosphorus (P) additions and grazer manipulations. Zooplankton (Acartia sp.) populations typical of temperate zone estuaries suppressed cyanobacteria, and their influence was direct through grazing rather than indirect on nutrient stoichiometry. Cyanobacterial abundance and heterocysts were low in treatments with no external P inputs. Concentrations of dissolved inorganic P comparable to those in Narragansett Bay were obtained only in P-fertilized mesocosms. Unlike previous estuarine mesocosm experiments with P fertilization, planktonic cyanobacteria grew and fixed N in our experimental systems. However, mean cell and heterocyst abundances under the most favorable conditions (high P, low N:P, and low grazers) were much lower than in comparable freshwater experiments, with N limitation maintained. These results support the hypothesis that intrinsic growth of heterocystous cyanobacteria in saline estuaries is slower than in freshwater, and that slower growth is unlikely to be due to systematic differences in P availability. Slow growth, combined with grazing, can severely limit development of planktonic, N-fixing cyanobacterial blooms in estuaries.

Philosophical Transactions of the Royal Society B, Dec 3, 2018

One contribution of 23 to a theme issue 'Salt in freshwaters: causes, ecological consequences and... more One contribution of 23 to a theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Limnology and Oceanography Bulletin, Jul 20, 2016

Socio-Ecological Practice Research, 2022

Aldo Leopold's essay, “Odyssey”, may have contributed to the development of the ecosystem con... more Aldo Leopold's essay, “Odyssey”, may have contributed to the development of the ecosystem concept and approach.

This dataset contains confirmed observations of mammal species at the Hubbard Brook Experimental ... more This dataset contains confirmed observations of mammal species at the Hubbard Brook Experimental Forest and adjacent Mirror Lake. The original is was published as Holmes, R. T. and G. E. Likens. 1999. Organisms of the Hubbard Brook Valley, New Hampshire. USDA Forest Service, Northeastern Research Station, General Tech. Report NE-257. 32 pp. The list is updated here (January 2021) to include additional species observed since the original publication, with annotated comments by R.T. Holmes, H. ter Hofstede (bats) and L. Christenson (from motion-detecting cameras, 2014-2019).

Hydrological Processes, 2021

Ecosystems constantly adjust to altered biogeochemical inputs, changes in vegetation and climate,... more Ecosystems constantly adjust to altered biogeochemical inputs, changes in vegetation and climate, and previous physical disturbances. Such disturbances create overlapping ‘biogeochemical legacies’ affecting modern nutrient mass balances. To understand how ‘legacies’ affected watershed‐ecosystem (WEC) biogeochemistry during five decades of studies within the Hubbard Brook Experimental Forest (HBEF), we extended biogeochemical trends and hydrologic fluxes back to 1900 to provide an historical framework for our long‐term studies. This reconstruction showed acid rain peaking at HBEF in the late 1960s‐early 1970s near the beginning of the Hubbard Brook Ecosystem Study (HBES). The long‐term, parabolic arc in acid inputs to HBEF generated a corresponding arc in the ionic strength of stream water, with acid inputs generating increased losses of H+ and soil base cations between 1963 and 1969 and then decreased losses after 1970. Nitrate release after disturbance is coupled with previous N‐de...

Hydrological Processes, 2020

As a graduate student, I studied circulation and mixing in lakes, but was fascinated by the numer... more As a graduate student, I studied circulation and mixing in lakes, but was fascinated by the numerous biological, geological and chemical (biogeochemical) interactions in lakes. I also had investigated the interactions and interconnections between catchments (watersheds), airsheds and lakes by releasing I into the depths of a meromictic (permanently stratified) lake in northern Wisconsin and then tracing its transport via emerging, flying adult midges (Chaoborus spp.) to the lake's shoreline and drainage basin (Hasler & Likens, 1963; Likens, 1962). The surprising finding about this connection (i.e., uphill transport of chemicals, sensu Leopold, 1949), provided my first direct insight into the existence and importance of these vital and interesting biogeochemical interactions and connections (air-land-water interactions). I began to study these interactions more formally when I moved to Dartmouth College in 1961 and initiated the Hubbard Brook Ecosystem Study (HBES) with Herb Bormann, Noye Johnson and Bob Pierce in 1963. Establishing boundaries for these ecosystems gave quantitative meaning to these studies. Likewise, the mass balance approach of the HBES (Watershed Ecosystem Concept WEC) (Bormann & Likens, 1967; Likens et al., 2021) applied to watershedecosystems of the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of NH, with carefully defined boundaries, provided a potent opportunity to combine hydrology and chemistry and obtain quantitative information on flux of nutrients into and out of adjacent watersheds. The WEC also enabled us to do experimental manipulations at large, catchment scales (an experiment [experimental manipulation] is one of the most powerful tools in science). Our USDA Forest Service partners in the HBES contributed continuous, quantitative, hydrologic data on precipitation amount and streamflow amount to this team effort. Moreover, the ability to do long-term (currently 57+ years and counting for the HBES) integrated biogeochemical and hydrological monitoring at a secure site, coupled with long-term, integrated ecosystem research, provided biogeochemical insights that were not available, or very difficult to obtain, otherwise (e.g., Bormann & Likens, 1967; Likens, 2013). Because of the large scale, watershed manipulation results also had management relevance (e.g., forestry practices, acid rain mitigation, role of organic debris dams in streams: Bormann & Likens, 1967; Bormann & Likens, 1979; Holmes & Likens, 2016; Likens & Bilby, 1982; Likens, 2010). The role of biology in these air-land-water interactions was demonstrated on many levels. An interesting biogeochemical example was the concentration and transport of dispersed, vital nutrients like calcium and phosphorus to ridge tops in moose antlers (Leopold's “uphill transport”) in these watershed-ecosystems (Likens, 2013). We initiated the WEC in 1963 (Bormann & Likens, 1967) using paired watershed-ecosystems at the HBEF (43 560N, 71 450W). A paired watershed approach does not provide a strict “control” needed in experimental studies (Likens, 1985), but does give critical reference information during whole watershed, experimental manipulations. Because these HBEF watersheds were relatively watertight regarding deep seepage (Bormann & Likens, 1967; Juang, 1966; Likens, 2013; Likens et al., 1967), mass balances could be done quantitatively. The difference between input of cations in precipitation and output in stream water also gave conservative, reasonable estimates of geochemical weathering at the watershed scale (Likens, 2013; Likens et al., 1967). Combining quantitative hydrology (precipitation and streamflow) with quantitative chemistry of precipitation and stream water enabled calculation of Net Hydrologic Flux (NHF). The strong effect of hydrology on NHF was demonstrated frequently in analyses of biogeochemical mass balances in these watershed-ecosystem studies (e.g., Likens et al., 1967; Likens et al., 2021). For example, drought and rewetting are major factors in accumulation, transport, and transformation of solutes in stream water (Likens et al., 2021). Quantitative mass balances represent the biogeochemical connection between small watershed-ecosystems and the larger biospheric systems of the Earth and help to identify the relevant connections pertinent to management intervention (Bormann & Likens, 1967). For example, streamwater outputs of phosphorus and nitrogen from a catchment may represent the major inputs of these critical nutrients for a receiving lake (e.g., Likens & Bormann, 1974). Whole watershed experimentation (such as the addition of the mineral, Wollastonite [CaSiO3], to Watershed 1 and removal of trees Received: 24 September 2020 Revised: 3 November 2020 Accepted: 9 November 2020

Biogeochemistry, 2016

This study evaluated the contribution of winter rain-on-snow (ROS) events to annual and seasonal ... more This study evaluated the contribution of winter rain-on-snow (ROS) events to annual and seasonal nitrate (N-NO 3) export and identified the regional meteorological drivers of inter-annual variability in ROS N-NO 3 export (ROS-N) at 9 headwater streams located across Ontario, Canada and the northeastern United States. Although on average only 3.3 % of annual precipitation fell as ROS during winter over the study period, these events contributed a significant proportion of annual and winter N-NO 3 export at the majority of sites (average of 12 and 42 %, respectively); with the exception of the most northern catchment, where total winter precipitation was exceptionally low (average 77 mm). In years with a greater magnitude of ROS events, the timing of the peak N-NO 3 export period (during spring melt) was redistributed to earlier in the year. Variability in ROS frequency and magnitude amongst sites was high and a generalised linear model demonstrated that this spatial variability could be explained by interactive effects between regional and site-specific drivers. Snowpack coverage was particularly important for explaining the site-specific ROS response. Specifically, ROS events were less common when higher temperatures eliminated snow cover despite increasing the proportion of winter rainfall, whereas ROS event frequency was greater at sites where sufficient snow cover remained.

Verhandlungen, Dec 1, 1990

The Hubbard Brook Ecosystem Study (HBES), begun in 1963, is an ongoing , longterm effort to under... more The Hubbard Brook Ecosystem Study (HBES), begun in 1963, is an ongoing , longterm effort to understand the structure and function of forest watersheds and associated aquatic ecosystems at the Hubbard Brook Experimental Forest in New Hampshire. Chemical analyses of streamwater and precipitation collections began in 1963, and analyses of lakewater collections began in 1967. This publication documents these collection methods, sites, and analytical techniques, providing a complete record to ensure the integrity of HBES data. The evolution of the HBES chemical data management system and the development of quality assurance procedures are described, as is the general algorithm by which ecosystem chemical inputs and outputs are calculated. These data represent a unique and important contribution to ecosystem science and provide an internationally recognized benchmark for assessing ecological changes.

Journal of Environmental Quality, May 1, 2000

The geographical and chemical origin of SO4deposition has become a concern, because anthropogeulc... more The geographical and chemical origin of SO4deposition has become a concern, because anthropogeulc S emissions have influenced the biogeochemistry of forested ecosystems and surface waters. Our aim was to evaluate the origin of SO~-in bulk precipitation at the Hubbard Brook Experimental Forest (HBEF), New Hampshire. We analyzed 26 years of archived bulk precipitation samples for sulfur stable isotopes. We compared the ~4S values with anthropogenic SOs emissions, the relative contribution of sea salt aerosols (as the SO42-fNa + ratio in precipitation), and temperature and solar radiation effects on the long-term patterns of fi34S values. The long-term pattern of ~4S values in bulk precipitation could be explained partly by the relative contribution of marine O−˜orsolarradiationbutnotbytemperaturevariationoranthropogenicSOsemissions.Thehighvariabilityofthefi4˜SvaluesofvariousfossilfuelsmakesitdifficulttousestableO~-or solar radiation but not by temperature variation or anthropogenic SOs emissions. The high variability of the fi~4S values of various fossil fuels makes it difficult to use stable O−˜​orsolarradiationbutnotbytemperaturevariationoranthropogenicSOsemissions.Thehighvariabilityofthefi4˜Svaluesofvariousfossilfuelsmakesitdifficulttousestable isotopes for identifying whether changing fossil fuel use is affecting the ~4S values in bulk precipitation. The seasonal pattern of fi34S values in bulk precipitation (significantly higher values in the winter than the summer) may be explained by the temperature dependence of the isotopic shift during SO42-formation in the atmosphere. A greater relative contribution of marine SO~ during the winter also may have contributed to the higher ~4S values in the winter. Previous investigations may have overestimated the role of biogenic emissions in affecting the fi34S pattern. I NOUSXR~AL~ZED regions of the world have been confronted with the consequences of acidic deposition since the beginning of the twentieth century. High SOl-deposition has resulted in SOl-accumulation in forest soils and acidification of surface waters. Despite the fact that SOl-deposition and SOl-concentrations in soil solutions and stream waters have been reduced considerably in northwestern Europe and eastern North

The Ithaca MAP3S Regional Precipitation Chemistry Site, in continuous operation since September 1... more The Ithaca MAP3S Regional Precipitation Chemistry Site, in continuous operation since September 1976 is now operating on a daily sampling rather than event sampling basis. Two other network stations (NDDN and EFPVMN) are co-located currently at the site. Research associated with MAP3S over the last year includes an analysis of the impact of changing emissions levels on precipitation chemistry in the eastern US. From 1977 to 1986 a 20% change in SOâ emissions and a 10% change in NO/sub x/ emissions have occurred over the eastern and midwestern US. Six continental precipitation chemistry sites from the MAP3S network, plus the Hubbard Brook Experimental Forest, New Hampshire, show a direct relationship between emission levels and precipitation concentrations, except for Penn State, Pennsylvania. MAP3S sites at Illinois and Ohio, located closest to the major SOâ source regions, demonstrate statistically significant (P < 0.05) linear regressions of SOâ concentrations on SOâ emissions. Hubbard Brook shows the strongest relationship (P < 0.01) between SOâ emissions and SOâ concentration in precipitation. Only Whiteface Mountain, New York, shows a significant relationships (P < 0.10) for NO/sub x/ emissions and NOâ/sup /minus// concentrations. However, Illinois, Ohio, Ithaca, and Hubbard Brook show significant linear regressions of H/sup +/ concentrations on emissions of SOâ + NO/sub x/ (P < 0.10, 0.05, 0.05, and 0.01, respectively). Overall, for the entire region examined, decreasing SOâ emission levels appear to have decreased SOâ concentrations with an efficiency of 66% + 17% (s.e.).

Ecology, Aug 1, 2017

The Hubbard Brook Ecosystem Study officially began on 1 June 1963. This archive contains the resu... more The Hubbard Brook Ecosystem Study officially began on 1 June 1963. This archive contains the results of 50 yr of collection and analysis of (at least) weekly stream water and precipitation samples obtained during the period 1963-2014 (from 1 June 1963 to 30 May 2013). Stream chemistry for the nine gauged watersheds and precipitation chemistry for precipitation gauges distributed throughout the Hubbard Brook Experimental Forest are reported as concentrations in (mg/L).

Science, Jun 14, 1974

At present, acid rain or snow is falling on most of the northeastern United States. The annual ac... more At present, acid rain or snow is falling on most of the northeastern United States. The annual acidity value averages about pH 4, but values between pH 2.1 and 5 have been recorded for individual storms. The acidity of precipitation in this region apparently increased about 20 years ago, and the increase may have been associated with the augmented use of natural gas and with the installation of particle-removal devices in tall smokestacks. Only some of the ecological and economic effects of this widespread introduction of strong acids into natural systems are known at present, but clearly they must be considered in proposals for new energy sources and in the development of air quality emission standards.

University of California Press eBooks, Nov 25, 2009

Water Resources Research, Dec 1, 1974

Analysis of recent precipitation samples from the northeastern United States has shown a consiste... more Analysis of recent precipitation samples from the northeastern United States has shown a consistent pH of less than 4.4, when the expected pH based upon equilibrium with CO2 would be 5.6. A stoichiometric formation process being assumed, some 65% of the acidity is due to H2SO4, 30% to HNO3, and less than 5% to HCl. The pH values may be predicted from chemical content and generally agree to within 0.1 pH unit with the observed pH. The distribution of acid precipitation encompasses most of the northeastern United States. This pattern apparently has existed since about 1950–1955, but the intensity of acid deposition, especially that due to HNO3, has increased since then. Analysis of prevailing winds indicates that much of the acidity originates as a general source over industrial areas in the Midwest.

Hydrological Processes, Jun 28, 2017

We introduce a new representation of coupled solute and water age dynamics at the catchment scale... more We introduce a new representation of coupled solute and water age dynamics at the catchment scale, which shows how the contributions of young runoff waters can be directly referenced to observed water quality patterns. The methodology stems from recent trends in hydrologic transport that acknowledge the dynamic nature of streamflow age and explores the use of water age fractions as an alternative to the mean age. The approach uses a travel time-based transport model to compute the fractions of streamflow that are younger than some thresholds (e.g., younger than a few weeks) and compares them to observed solute concentration patterns. The method is here validated with data from the Hubbard Brook Experimental Forest during spring 2008, where we show that the presence of water younger than roughly 2 weeks, tracked using a hydrologic transport model and deuterium measurements, mimics the variation in dissolved silicon concentrations. Our approach suggests that an age-discharge relationship can be coupled to classic concentration-discharge relationship, to identify the links between transport timescales and solute concentration. Our results highlight that the younger streamflow components can be crucial for determining water quality variations and for characterizing the dominant hydrologic transport dynamics.

Marine Ecology Progress Series, Mar 15, 2006

Heterocystous, planktonic cyanobacteria capable of fixing atmospheric N 2 into available nitrogen... more Heterocystous, planktonic cyanobacteria capable of fixing atmospheric N 2 into available nitrogen (N) are common and critically important to nutrient cycling in many lakes, yet they are rarely observed in estuaries at salinities >10 ppt, even when strongly N limited. In a series of mesocosm experiments using water from Narragansett Bay (Rhode Island), we manipulated top-down (grazing) and bottom-up (nutrient) factors hypothesized to exclude heterocystous cyanobacteria from estuaries. We previously reported that planktonic, heterocystous cyanobacteria grew and fixed N in the absence of grazers. Here, we focus on responses to phosphorus (P) additions and grazer manipulations. Zooplankton (Acartia sp.) populations typical of temperate zone estuaries suppressed cyanobacteria, and their influence was direct through grazing rather than indirect on nutrient stoichiometry. Cyanobacterial abundance and heterocysts were low in treatments with no external P inputs. Concentrations of dissolved inorganic P comparable to those in Narragansett Bay were obtained only in P-fertilized mesocosms. Unlike previous estuarine mesocosm experiments with P fertilization, planktonic cyanobacteria grew and fixed N in our experimental systems. However, mean cell and heterocyst abundances under the most favorable conditions (high P, low N:P, and low grazers) were much lower than in comparable freshwater experiments, with N limitation maintained. These results support the hypothesis that intrinsic growth of heterocystous cyanobacteria in saline estuaries is slower than in freshwater, and that slower growth is unlikely to be due to systematic differences in P availability. Slow growth, combined with grazing, can severely limit development of planktonic, N-fixing cyanobacterial blooms in estuaries.

Philosophical Transactions of the Royal Society B, Dec 3, 2018

One contribution of 23 to a theme issue 'Salt in freshwaters: causes, ecological consequences and... more One contribution of 23 to a theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Limnology and Oceanography Bulletin, Jul 20, 2016

Socio-Ecological Practice Research, 2022

Aldo Leopold's essay, “Odyssey”, may have contributed to the development of the ecosystem con... more Aldo Leopold's essay, “Odyssey”, may have contributed to the development of the ecosystem concept and approach.

This dataset contains confirmed observations of mammal species at the Hubbard Brook Experimental ... more This dataset contains confirmed observations of mammal species at the Hubbard Brook Experimental Forest and adjacent Mirror Lake. The original is was published as Holmes, R. T. and G. E. Likens. 1999. Organisms of the Hubbard Brook Valley, New Hampshire. USDA Forest Service, Northeastern Research Station, General Tech. Report NE-257. 32 pp. The list is updated here (January 2021) to include additional species observed since the original publication, with annotated comments by R.T. Holmes, H. ter Hofstede (bats) and L. Christenson (from motion-detecting cameras, 2014-2019).

Hydrological Processes, 2021

Ecosystems constantly adjust to altered biogeochemical inputs, changes in vegetation and climate,... more Ecosystems constantly adjust to altered biogeochemical inputs, changes in vegetation and climate, and previous physical disturbances. Such disturbances create overlapping ‘biogeochemical legacies’ affecting modern nutrient mass balances. To understand how ‘legacies’ affected watershed‐ecosystem (WEC) biogeochemistry during five decades of studies within the Hubbard Brook Experimental Forest (HBEF), we extended biogeochemical trends and hydrologic fluxes back to 1900 to provide an historical framework for our long‐term studies. This reconstruction showed acid rain peaking at HBEF in the late 1960s‐early 1970s near the beginning of the Hubbard Brook Ecosystem Study (HBES). The long‐term, parabolic arc in acid inputs to HBEF generated a corresponding arc in the ionic strength of stream water, with acid inputs generating increased losses of H+ and soil base cations between 1963 and 1969 and then decreased losses after 1970. Nitrate release after disturbance is coupled with previous N‐de...

Hydrological Processes, 2020

As a graduate student, I studied circulation and mixing in lakes, but was fascinated by the numer... more As a graduate student, I studied circulation and mixing in lakes, but was fascinated by the numerous biological, geological and chemical (biogeochemical) interactions in lakes. I also had investigated the interactions and interconnections between catchments (watersheds), airsheds and lakes by releasing I into the depths of a meromictic (permanently stratified) lake in northern Wisconsin and then tracing its transport via emerging, flying adult midges (Chaoborus spp.) to the lake's shoreline and drainage basin (Hasler & Likens, 1963; Likens, 1962). The surprising finding about this connection (i.e., uphill transport of chemicals, sensu Leopold, 1949), provided my first direct insight into the existence and importance of these vital and interesting biogeochemical interactions and connections (air-land-water interactions). I began to study these interactions more formally when I moved to Dartmouth College in 1961 and initiated the Hubbard Brook Ecosystem Study (HBES) with Herb Bormann, Noye Johnson and Bob Pierce in 1963. Establishing boundaries for these ecosystems gave quantitative meaning to these studies. Likewise, the mass balance approach of the HBES (Watershed Ecosystem Concept WEC) (Bormann & Likens, 1967; Likens et al., 2021) applied to watershedecosystems of the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of NH, with carefully defined boundaries, provided a potent opportunity to combine hydrology and chemistry and obtain quantitative information on flux of nutrients into and out of adjacent watersheds. The WEC also enabled us to do experimental manipulations at large, catchment scales (an experiment [experimental manipulation] is one of the most powerful tools in science). Our USDA Forest Service partners in the HBES contributed continuous, quantitative, hydrologic data on precipitation amount and streamflow amount to this team effort. Moreover, the ability to do long-term (currently 57+ years and counting for the HBES) integrated biogeochemical and hydrological monitoring at a secure site, coupled with long-term, integrated ecosystem research, provided biogeochemical insights that were not available, or very difficult to obtain, otherwise (e.g., Bormann & Likens, 1967; Likens, 2013). Because of the large scale, watershed manipulation results also had management relevance (e.g., forestry practices, acid rain mitigation, role of organic debris dams in streams: Bormann & Likens, 1967; Bormann & Likens, 1979; Holmes & Likens, 2016; Likens & Bilby, 1982; Likens, 2010). The role of biology in these air-land-water interactions was demonstrated on many levels. An interesting biogeochemical example was the concentration and transport of dispersed, vital nutrients like calcium and phosphorus to ridge tops in moose antlers (Leopold's “uphill transport”) in these watershed-ecosystems (Likens, 2013). We initiated the WEC in 1963 (Bormann & Likens, 1967) using paired watershed-ecosystems at the HBEF (43 560N, 71 450W). A paired watershed approach does not provide a strict “control” needed in experimental studies (Likens, 1985), but does give critical reference information during whole watershed, experimental manipulations. Because these HBEF watersheds were relatively watertight regarding deep seepage (Bormann & Likens, 1967; Juang, 1966; Likens, 2013; Likens et al., 1967), mass balances could be done quantitatively. The difference between input of cations in precipitation and output in stream water also gave conservative, reasonable estimates of geochemical weathering at the watershed scale (Likens, 2013; Likens et al., 1967). Combining quantitative hydrology (precipitation and streamflow) with quantitative chemistry of precipitation and stream water enabled calculation of Net Hydrologic Flux (NHF). The strong effect of hydrology on NHF was demonstrated frequently in analyses of biogeochemical mass balances in these watershed-ecosystem studies (e.g., Likens et al., 1967; Likens et al., 2021). For example, drought and rewetting are major factors in accumulation, transport, and transformation of solutes in stream water (Likens et al., 2021). Quantitative mass balances represent the biogeochemical connection between small watershed-ecosystems and the larger biospheric systems of the Earth and help to identify the relevant connections pertinent to management intervention (Bormann & Likens, 1967). For example, streamwater outputs of phosphorus and nitrogen from a catchment may represent the major inputs of these critical nutrients for a receiving lake (e.g., Likens & Bormann, 1974). Whole watershed experimentation (such as the addition of the mineral, Wollastonite [CaSiO3], to Watershed 1 and removal of trees Received: 24 September 2020 Revised: 3 November 2020 Accepted: 9 November 2020

Biogeochemistry, 2016

This study evaluated the contribution of winter rain-on-snow (ROS) events to annual and seasonal ... more This study evaluated the contribution of winter rain-on-snow (ROS) events to annual and seasonal nitrate (N-NO 3) export and identified the regional meteorological drivers of inter-annual variability in ROS N-NO 3 export (ROS-N) at 9 headwater streams located across Ontario, Canada and the northeastern United States. Although on average only 3.3 % of annual precipitation fell as ROS during winter over the study period, these events contributed a significant proportion of annual and winter N-NO 3 export at the majority of sites (average of 12 and 42 %, respectively); with the exception of the most northern catchment, where total winter precipitation was exceptionally low (average 77 mm). In years with a greater magnitude of ROS events, the timing of the peak N-NO 3 export period (during spring melt) was redistributed to earlier in the year. Variability in ROS frequency and magnitude amongst sites was high and a generalised linear model demonstrated that this spatial variability could be explained by interactive effects between regional and site-specific drivers. Snowpack coverage was particularly important for explaining the site-specific ROS response. Specifically, ROS events were less common when higher temperatures eliminated snow cover despite increasing the proportion of winter rainfall, whereas ROS event frequency was greater at sites where sufficient snow cover remained.