Enteromorpha and the cycling of nitrogen in a small estuary (original) (raw)
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Journal of Experimental Marine Biology and Ecology, 1998
We explored the use of an opportunistic green alga, Enteromorpha intestinalis (L. Link), as an indicator of N enrichment in a southern California salt marsh. In conjunction with N additions to cordgrass (Spartina foliosa, Trin) in April, June and August 1995, mesh bags containing N-starved algal tissue were placed within cordgrass patches, at their edges along islands, and in adjacent channels. After 1 week in the field, recovered algal tissue was used to test detection of two levels of total N supply (one twice as high as the other), as well as no added N (control). Tissue N concentration, calculated as the percentage change in N, was the best of several algal measures at discerning differences in N availability in any month. In both April and June, tissue N declined from the marsh plain to the channels, reflecting declining N supply. Tissue N concentration also reflected differences in the total quantity of N added. Within the channels adjacent to fertilized areas, algal tissue N was similar to control areas, suggesting that N additions to cordgrass are not resulting in eutrophication of open waters. In August, the algae detected N additions on the marsh plain, but survivorship was poor; other algal species may be better indicators of enrichment in late-summer. With further investigation, the technique presented in this paper has the potential to be developed into a useful bioassay for detecting eutrophication of coastal salt marshes and lagoons.
Estuarine, Coastal and Shelf Science, 2006
Proliferation of fast growing ephemeral macroalgae may occur in intertidal environments and potentially affect the annual gross (GPP a ) and net (NPP a ) primary production of the system. Seasonal macroalgal proliferation was studied in situ in the Roscoff Aber bay and its influence on the annual benthic metabolism was investigated during low tide. CO 2 exchanges at the air-sediment interface were regularly measured within a benthic chamber in order to calculate in situ net (NPP), gross (GPP) primary production and benthic community respiration (BCR). These measurements were assessed on bare sediments at 3 representative sampling sites and in an additional sampling site regularly affected by macroalgae deposit. On bare sediments, under optimal irradiance daily GPP and NPP exhibited fortnightly fluctuations. Annual net primary production (NPP a ) was net autotrophic at the coarsest sites (up to 16 gC m À2 y À1 ) and net heterotrophic at the muddiest station (up to À22 gC m À2 y À1 ). On macroalgal mats GPP and BCR increased respectively from 3 to 10 and 3 to 20 times compared to bare sediments. This indicated that, at an hourly scale, the impact of macroalgae deposit on benthic metabolism was very significant. However, at the annual scale, macroalgae deposit and sediment microalgae respectively accounted for 12% and 88% of the annual net benthic primary production indicating that macroalgae proliferation poorly affected the annual carbon budget.
Estuaries, 2004
We conducted a laboratory experiment to quantify nutrient (nitrogen and phosphorus) limitation of macroalgae collected along a gradient in water column nutrient availability in Upper Newport Bay estuary, a relatively nutrient-rich system in southern California, United States. We collectedEnteromorpha intestinalis and water for use in the experiment from five sites ranging from the lower end of the estuary to the head. Initial algal tissue N and P concentrations and molar N∶P ratios—as well as water column NO3 and total Kjeldahl nitrogen (TKN)—increased along a spatial gradient from the lower end toward the head. Water column soluble reactive phosphorus (SRP) varied among sites as well but did not follow a pattem of increasing from the seaward end toward the head. Algae from each site were assigned to one of four experimental treatments: control (C), nitrogen enrichment (+N), phosphorus enrichment (+P), and nitrogen and phosphorus enrichment (+N+P). Each week for 3 wk we replaced the water in each unit with the appropriate treatment water to mimic a poorly flushed estuary. After 3 wk, the degree of nutrient limitation ofE. intestinalis varied spatially with distance from the head of the estuary. Growth ofE. intestinalis collected from several sites increased with N enrichment alone and increased further when P was added in combination with N This indicated that N was limiting and that when N was sufficient, P became limiting. Sites from whichE. intestinalis exhibited nutrient limitation spanned the range of background water column NO3 (12.9±0.4 to 55.2±2.1 μM) and SRP (0.8±0.0 to 2.9±0.2 μM) concentrations. Algae that were N limited had initial tissue N levels ranging from 1.18±0.03 to 2.81±0.08% dry weight and molar N∶P ratios ranging from 16.75±0.39 to 26.40±1.98.
Enteromorpha intestinalis and Ulva expansa were investigated in two separate experiments. To measure uptake rates over a range of conditions, we varied initial water column NO 3 concentrations (low, medium, and high) and initial algal tissue nutrient status (enriched versus depleted). Uptake rates were determined by measuring the disappearance of NO 3 from solution over time (1, 2, 4, 8, 12, and 24 h). E. intestinalis and U. expansa exhibited a high affinity for N. In the low water column concentration treatments, E. intestinalis and U. expansa removed all measurable NO 3 from the water within 8 h and 12 h, respectively. Nutrient-depleted algae consistently removed more NO 3 than enriched algae over each sampling interval. For E. intestinalis, maximum rates of NO 3 uptake increased with increasing initial water column nutrient concentrations, indicating a relationship between uptake and external substrate concentration. The same was true for U. expansa in the low and medium water column nutrient treatments. Maximum rates of NO 3 uptake exceeded 200 µmoles g dry wt -1 h -1 by E. intestinalis and 125 µmoles g dry wt -1 h -1 by U.
Marine Ecology Progress Series, 2000
Sedimentary organic matter mineralisation (oxygen uptake), nitrogen (N) loss (denitrification) and nutrient exchange were measured seasonally in areas of both high and low Enteromorpha sp. and Ulva sp. cover at 6 sites in 2 harbours on the south coast of England. Measurements of macroalgal and phytoplankton photosynthesis were also carried out. Sedimentary carbon (C) and N cycling was most rapid at the sites with a heavy cover of macroalgae. Macroalgae were responsible, on average, for 57% of total dark oxygen uptake, with sediment bacterial respiration accounting for the remaining 43%. Dark rates of nutrient uptake for Enteromorpha sp. and Ulva sp. were equivalent to 70% of those in the light. Denitrification rates were low (D w [NO 3 from overlying water] < 35, D n [coupled to sedimentary nitrification] < 26 µmol N m -2 h -1 ) throughout the harbours, and represented a minor sink for N. Coupled nitrification-denitrification (D n ) could, on average, account for only 0.3 to 1.7% of the calculated rate of N mineralised within the sediment, suggesting that the vast majority of N (> 98%) remained within the system. External inputs of nutrients (N and P) to the harbours may have supported the spring growth of macroalgae, but it seemed unlikely that they were capable of supporting the summer peaks in algal biomass and rapid rates of N turnover. More likely the intense recycling (ammonification) of organically bound N within the sediments, coupled to a minimum loss via denitrification, provided a sustained and sufficient N supply for the macroalgae.
Concentrations of nitrogen in sandy sediments of a eutrophic estuarine lagoon
Hydrobiologia, 1998
Concentrations of sediment organic nitrogen, dissolved inorganic nitrogen (ammonium, nitrite and nitrate), and dissolved organic nitrogen (DON) in sediments were measured at two sites in a eutrophic estuarine lagoon. One is a shallow aerobic site where macrobenthos are abundant and the other is a deep anaerobic site devoid of macrobenthos. Four species of macrobenthos (Bivalvia: Corbicula japonica, Annelida: Notomastus sp., Neanthes japonica and Oligochaeta sp.) were found in 8 sandy sediment cores collected at a shallow site in three succcessive summers. DON (170-1500 µg atom N l −1 ) was the major constituent of dissolved nitrogen with 10 times greater concentration than ammonium (55-180 µg atom N l −1 ) and 1000 times greater than nitrate (0.14-5.9 µg atom N l −1 ) and nitrite (0.21-1.4 µg atom N l −1 ). The ammonium content in anaerobic muddy sediments at the deep site (210-350 µg atom N l −1 ) was higher than in aerobic sandy sediments, whereas DON was higher in aerobic sediments than anaerobic sediments (90-240 µg atom N l −1 ). In aerobic sediments, depth profiles of DIN were nearly constant whereas DON was mostly highest at the surface. On the other hand, the increase of DON and ammonium was observed where macrobenthos was found. The occurrence of macrobenthos and high content of DON and ammonium content in the layers of sediment may suggest the influence of macrobenthos in the partitioning of nitrogen species through their motion and excretion.
Marine Ecology Progress Series, 2004
Benthic fluxes of dissolved nitrogen, rates of denitrification, N 2 fixation and NH 4 + upward flux within the sediment (calculated from porewater profiles) were measured on the upper and lower mudflats at 2 study sites, 1 in the upper, river-dominated part of the estuary, and 1 in the lower, more marine part of the Huon Estuary, Tasmania, Australia. The calculated upward flux of NH 4 + from within the sediment based on porewater profiles was generally in excess of measured benthic fluxes, suggesting that NH 4 + was reassimilated at the sediment surface by microphytobenthos (MPB). The ratio of total CO 2 (TCO 2 ):NH 4 + produced within the sediment was generally in excess of 15, and in some cases in excess of 60. Significant influxes and effluxes of dissolved organic nitrogen (DON) were measured where the activity of MPB was highest. At times, DON influxes and effluxes were well in excess of dissolved inorganic nitrogen (DIN) fluxes, highlighting the importance of measuring DON fluxes where the activity of MPB is high. Rates of denitrification were very low, and represented only a small loss of N from the sediment, most probably as a consequence of the activity of MPB. Estimates of nitrogen assimilation by MPB showed that N 2 fixation was likely to be the major source of nitrogen during the summer at the study site in the upper estuary. There was also a high estimated C:N ratio (~20) of TCO 2 and nitrogen assimilated at this site, suggesting that a significant proportion of primary production was exuded as dissolved organic carbon rather than cellular production.
Aquatic Ecology, 2004
Large blooms of opportunistic green macroalgae such as Enteromorpha intestinalis are of ecological concern in estuaries worldwide. Macroalgae derive their nutrients from the water column but estuarine sediments may also be an important nutrient source. We hypothesized that the importance of these nutrient sources to E. intestinalis varies along a nutrient-resource gradient within an estuary. We tested this in experimental units constructed with water and sediments collected from 3 sites in Upper Newport Bay estuary, California, US, that varied greatly in water column nutrient concentrations. For each site there were three treatments: sediments + water; sediments + water + Enteromorpha intestinalis (algae); inert sand + water + algae. Water in units was exchanged weekly simulating low turnover characteristic of poorly flushed estuaries. The importance of the water column versus sediments as a source of nutrients to E. intestinalis varied with the magnitude of the different sources. When initial water column levels of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) were low, estuarine sediments increased E. intestinalis growth and tissue nutrient content. In experimental units from sites where initial water column DIN was high, there was no effect of estuarine sediments on E. intestinalis growth or tissue N content. Salinity, however, was low in these units and may have inhibited growth. E. intestinalis growth and tissue P content were highest in units from the site with highest initial sediment nutrient content. Water column DIN was depleted each week of the experiment. Thus, the water column was a primary source of nutrients to the algae when water column nutrient supply was high, and the sediments supplemented nutrient supply to the algae when water column nutrient sources were low. Depletion of water column DIN in sediment + water units indicated that the sediments may have acted as a nutrient sink in the absence of macroalgae. Our data provide direct experimental evidence that macroalgae utilize and ecologically benefit from nutrients stored in estuarine sediments.
Marine Pollution Bulletin, 2007
A spatially dynamic model for the productivity of spores and adults of green macroalgae (Enteromorpha sp.) was developed for a mesotidal estuary (Mondego estuary, Portugal). Many of the algal processes and parameters included in the model were experimentally obtained. Model predictions were compared to a real time series (1993)(1994)(1995)(1996)(1997) of macroalgal biomass variation and the two sets show a good agreement (ANOVA, P < 0.001). Results suggest that algal growth is highly sensitive to small changes in depth and exhibits different patterns of variation in different seasons. On a yearly basis, global calculations for the south channel of the estuary (137 ha) suggest that during bloom years, macroalgal biomass may reach about 21,205 ton DW compared to 240 ton DW in regular years. On a seasonal basis, the difference may be even more significant. The consequences of such variations on the nitrogen and phosphorus loading of the system and the adjacent coastal area are discussed.