Changes in submerged aquatic vegetation (SAV) coverage caused by extended drought and flood pulses (original) (raw)
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Extreme water-level fluctuations determine aquatic vegetation in modified large-river floodplains
2005
Water bodies in large-river floodplains are typically dominated by aquatic vegetation. The proportion of macrophyte-dominated lakes varies between years, depending on annually different water-level fluctuations within the lakes. We reanalysed aquatic-vegetation inventories made over five decades in floodplain lakes along the Lower Rhine, and related them to summer inundation and drawdown events. We observed a lower probability of submerged macrophyte dominance (lake cover > 20 %) after inundation in summer, with contrasting responses for different species. Lake-bottom exposure during prolonged low water stages had an opposite effect, resulting in an increased probability of dominance by submerged vegetation and a decrease of nymphaeid vegetation. Our results indicate that under the current, hydromorphologically modified, conditions a small proportion of water bodies in the floodplains has abundant aquatic vegetation, unless new sites are repeatedly created which provide opportunities for colonization. The results are important for management as they help in defining the ecological status of floodplain lakes.
Hydrobiologia, 2018
Lakes and reservoirs are important sites for biogeochemical cycling on both regional and global scales. Shallow lakes often have higher coverage of submerged aquatic vegetation (SAV) because of increased light penetration to the sediment as well as stronger interactions between the sediment and the water column. These biotic and abiotic interactions can strongly affect nutrient cycling. This study evaluated how hydrologically driven changes in SAV coverage affected nutrient processing within a relatively shallow reservoir. To assess these effects, a comprehensive water quality sampling network was established that quantified nutrient concentrations in the inflows and outflow of the lake. Annual vegetation surveys quantified the spatial coverage of SAV. Annual inflow was significantly lower in the first year of the study compared to the following 2 years. Consequently, SAV coverage was also highest during the lowest flows in the first year and was lower in the following 2 years when flows were greater. NO 3-N concentrations were also lowest within Hydrilla beds and in the outflow during the growing season of the first year. Our results suggest that hydrological variation was the main driving variable of SAV coverage, and that the extent of SAV coverage strongly controlled nutrient processing at the whole-reservoir scale.
Aquatic Botany, 2014
Most studies suggest that floods remove substantial plant biomass due to mechanical forces applied during peak flows, thus contributing to the structuring of riverine vegetation. Effects on biomass were tested via an in situ experiment in the backwater of a large upland river in Scotland where frequency of connection to the main channel during floods controlled exposure to potential mechanical disturbance. Four macrophyte species (Potamogeton natans L., Myriophyllum alterniflorum DC., Ranunculus flammula L. and Mentha aquatica L.) were grown in trays and exposed to floods of different amplitude. Trays were distributed between an adjacent non-flooded control and the intermittently flooded backwater that differed principally in exposure to floods. The four taxa combined post-flooding biomass was surprisingly insensitive to floods, including two large events with recurrence intervals of 10-30 years. The four species showed different responses to flooding but only M. aquatica experienced a significant but small biomass reduction relative to control. Differences in biomass between control and backwater were mostly nonsignificant and did not vary with flood amplitude or spatially within the flooded backwater, with the exception of amphibious species that were disproportionately affected in the most disturbed upstream part. The macrophyte assemblage was generally more sensitive to winter than summer floods. This study indicates that macrophytes can limit significant biomass loss during major floods, and that this as with other disturbances, is likely to promote species coexistence.
Regulated Rivers: Research & …, 1998
Low frequency but high intensity events, such as severe floods or droughts, may have long-lasting effects on the structure and function of lotic ecosystems, as well as on man-made structures and human uses of rivers, floodplains, and estuaries. In the summer of 1993, major, global-scale atmospheric circulation anomalies caused unusual precipitation in the upper midwestern part of the US (return frequencies ranged from 75 to 300 years, dependent on location), creating extreme flooding (100-500-year) along the upper Mississippi River, the Illinois River, and the lower Missouri River, and many smaller tributaries US Army Corps of Engineers, 1995). In the same year and early in 1994 there also were record floods in many of the large rivers of western Europe. A symposium in August 1995 at the annual meeting of the Ecological Society of America in Snowbird, Utah, brought together researchers who either had ecological studies on-going when extreme hydrologic events occurred or responded to an event. Of the eight papers presented at the symposium, four were submitted for this volume. Two papers not presented at the symposium are included here because they are relevant to the topic of extreme hydrologic events van Oorschot et al., submitted).
Aquatic Sciences, 2014
In floodplains located in temperate regions, seasonal variations in temperature affect biological communities and these effects may overlap with those of the flood regime. In this study we explored if and how timing (with regard to temperature seasonality) influences the responses of planktonic and free-floating plants communities to floods in a warm temperate floodplain lake and assessed its relevance for determining state shifts. We took samples of zooplankton, phytoplankton, picoplankton, heterotrophic nanoflagellates and free-floating macrophytes at four sites of the lake characterized by the presence-absence of emergent or free-floating macrophytes along a 2-year period with marked hydrological fluctuations associated to river flood dynamics. We performed ANOVA tests to compare the responses of these communities to floods in cold and warm seasons and among sites. Planktonic communities developed high abundances in response to floods that occurred in the cold season, while the growth of free-floating macrophytes was impaired by low winter temperatures. Spring and summer floods favored profuse colonization by free-floating plants and limited the development of planktonic communities. The prolonged absence of floods during warm periods caused environmental conditions that favored Cyanobacteria growth, leading to a ''low turbid waters'' regime. The occurrence of floods early in the warm season caused phytoplankton dilution and promoted free-floating plant colonization and a shift towards a ''high clear waters'' state. Zooplankton:phytoplankton biomass ratio was very low during floods in warm seasons, thus zooplankton grazing on phytoplankton seemed to play a minor role in the maintenance of the clear regime.
The role of floods and droughts on riverine ecosystems under a changing climate
Fisheries Management and Ecology, 2019
Floods and droughts are key driving forces shaping aquatic ecosystems. Climate change may alter key attributes of these events and consequently health and distribution of aquatic species. Improved knowledge of biological responses to different types of floods and droughts in rivers should allow the better prediction of the ecological consequences of climate change‐induced flow alterations. This review highlights that in unmodified ecosystems, the intensity and direction of biological impacts of floods and droughts vary, but the overall consequence is an increase in biological diversity and ecosystem health. To predict the impact of climate change, metrics that allow the quantitative linking of physical disturbance attributes to the directions and intensities of biological impacts are needed. The link between habitat change and the character of biological response is provided by the frequency of occurrence of the river wave characteristic—that is the event's predictability. The s...
The impact of flooding on aquatic ecosystem services
Biogeochemistry
Flooding is a major disturbance that impacts aquatic ecosystems and the ecosystem services that they provide. Predicted increases in global flood risk due to land use change and water cycle intensification will likely only increase the frequency and severity of these impacts. Extreme flooding events can cause loss of life and significant destruction to property and infrastructure, effects that are easily recognized and frequently reported in the media. However, flooding also has many other effects on people through freshwater aquatic ecosystem services, which often go unrecognized because they are less evident and can be difficult to evaluate. Here, we identify the effects that small magnitude frequently occurring floods (\ 10-year recurrence interval) and extreme floods ([ 100-year recurrence interval) have on ten aquatic ecosystem services through a systematic literature review. We focused on ecosystem services considered by the Millennium Ecosystem Assessment including: (1) supporting services (primary production, soil formation), (2) regulating services (water regulation, water quality, disease regulation, climate regulation), (3) provisioning services (drinking water, food supply), and (4) cultural services (aesthetic value, recreation and tourism). The literature search resulted in 117 studies and each of the Responsible Editor: Sujay Kaushal.
Experimental Floods Cause Ecosystem Regime Shift in a Regulated River
Ecological Applications, 2008
Reservoirs have altered the flow regime of most rivers on the globe. To simulate the natural flow regime, experimental floods are being implemented on regulated rivers throughout the world to improve their ecological integrity. As a large-scale disturbance, the long-term sequential use of floods provides an excellent empirical approach to examine ecosystem regime shifts in rivers. This study evaluated the long-term effects of floods (15 floods over eight years) on a regulated river. We hypothesized that sequential floods over time would cause a regime shift in the ecosystem. The floods resulted in little change in the physicochemistry of the river, although particulate organic carbon and particulate phosphorus were lower after the floods. The floods eliminated moss cover on bed sediments within the first year of flooding and maintained low periphyton biomass and benthic organic matter after the third year of flooding. Organic matter in transport was reduced after the third year of flooding, although peaks were still observed during rain events due to tributary inputs and side slopes. The floods reduced macroinvertebrate richness and biomass after the first year of floods, but density was not reduced until the third year. The individual mass of invertebrates decreased by about one-half after the floods. Specific taxa displayed either a loss in abundance, or an increase in abundance, or an increase followed by a loss after the third year. The first three flood years were periods of nonequilibrium with coefficients of variation in all measured parameters increasing two to five times from those before the floods. Coefficients of variation decreased after the third year, although they were still higher than before the floods. Analysis of concordance using Kendall's W confirmed the temporal changes observed in macroinvertebrate assemblage structure. An assessment of individual flood effects showed that later floods had ;30% less effect on macroinvertebrates than early floods of similar magnitude, suggesting that the new assemblage structure is more resilient to flood disturbance. We conclude that the floods caused an ecosystem regime shift that took three years to unfold. Additional long-term changes or shifts are expected as new taxa colonize the river from other sources.
Lynch_et_al-2018-Freshwater_Biology.pdf
1. Drought and summer drying can have strong effects on abiotic and biotic components of stream ecosystems. Environmental flow-ecology relationships may be affected by drought and drying, adding further uncertainty to the already complex interaction of flow with other environmental variables, including geomorphology and water quality.