Altered Hydrologic Regime Research Articles

Sedimentation and associated trace metal enrichment in the riparian zone of the Three Gorges Reservoir, China

Impoundment of the Three Gorges Reservoir has created an artificial riparian zone with a vertical height of 30m and a total area of 349km2, which has been subjected to seasonal inundation and exposure due to regular reservoir impoundment and the occurrence of natural floods. The significant alteration of hydrologic regime has caused numerous environmental changes. The present study investigated the magnitude and spatial pattern of sedimentation and metal enrichment in a typical section of the riparian zone, composed of bench terraces with previous agricultural land uses, and explored their links to the changed hydrologic regime. In particular, we measured the total sediment depths and collected surface riparian sediments and down-profile sectioned riparian soils (at 5cm intervals) for trace metal determination. Our analysis showed that the annual average sedimentation rates varied from 0.5 to 10cm·yr−1 and they decreased significantly with increasing elevation. This lateral distribution was principally attributed to seasonal variations in water levels and suspended sediment concentrations. Enriched concentrations of trace metals were found both in the riparian sediments and soils, but they were generally higher in the riparian sediments than in riparian soils and followed a similar lateral decreasing trend. Metal contamination assessment showed that the riparian sediments were slightly contaminated by Ni, Zn, and Pb, moderately contaminated by Cu, and moderately to strongly contaminated by Cd; while riparian soils were slightly contaminated by As, and moderately contaminated by Cd. Trace metal enrichment in the riparian sediments may be attributed to external input of contaminated sediments produced from upstream anthropogenic sources and chemical adsorption from dissolved fractions during pure sediment mobilization and after sink for a prolonged flooding period due to reservoir impoundment.

Potential future climate effects on mountain hydrology, stream temperature, and native salmonid life history

Native salmonids of western North America are subject to many environmental pressures, most notably the effects of introduced species and environmental degradation. To better understand how native salmonids on the eastern slopes of the Canadian Rocky Mountains may respond to future changes in climate, we applied a process-based approach to hydrologic and stream temperature modelling. This study demonstrates that stream thermal regimes in western Alberta, Canada, may only warm during the summer period, while colder thermal regimes during spring, fall, and winter could result from response to earlier onset of spring freshet. Model results of future climate impacts on hydrology and stream temperature are corroborated by an intercatchment comparison of stream temperature, air temperature, and hydrological conditions. Earlier fry emergence as a result of altered hydrological and thermal regimes may favour native westslope cutthroat trout (Oncorhynchus clarkii lewisii) in isolated headwater streams. Colder winter stream temperatures could result in longer incubation periods for native bull trout (Salvelinus confluentus) and limit threatened westslope cutthroat trout habitat.

Effect of hydrologic regime and forest age on Collembola in riparian forests

The principal objective of the study was to assess factors of primary importance for collembolan community variability measured in riparian forest stands of different age after traditional clear cutting within natural and altered hydrologic regimes. The study was conducted in the Ukrainian part of the Latorica river floodplain where the largest stands of the highly protected medio-European Querco—Ulmetum minoris fluvial forests can be found. Six oak forest stands were investigated on the river floodplain: three in a natural section (inside levee) of the floodplain, which have their original features preserved with periodical inundation, and three in a section separated by a flood control embankment (outside levee) and subjected to serious damage by drainage. In each section the three stands sampled were represented by different ages regenerated with clear-cutting (>3 years, >8 years and >112 years).Differences in hydrologic regimes were central to identification of a predictable and explainable percentage of variation in species composition of Collembola communities in fluvial forests. The hydrologic regime factor was correlated with the basic structural attributes of collembolan communities, such as abundance, species richness and some ecological traits. Season accounted for a higher degree of variation in collembolan communities than did the age of forest stands. We conclude that differences in hydrologic regime are of much higher importance in structuring collembolan communities in riparian forests than are the ages of stands.

Editorial

Editorial

Spatio-temporal changes of hydro-chemical parameters in the estuarine part of the River Ganges under altered hydrological regime and its impact on biotic communities

Hooghly estuary, the lowermost part of River Ganges in India, following the construction of Farakka barrage in 1975, witnessed improved freshwater inflow in the estuarine stretch of the river with significant impact on the salinity regime, water transparency, suspended sediments and nutrient load leading to alternations in the distribution and abundance of fish and other biotic organisms like plankton and benthos. A detailed seasonal study was conducted in Hooghly estuary during 2010–2012 to evaluate the spatio-temporal changes in selected physico-chemical parameters like temperature, transparency, pH, free CO2, dissolved oxygen, specific conductivity, total alkalinity, total hardness, salinity, available nutrients like nitrate, phosphate and silicate under the present hydrological regime in determining the distribution of fish and other aquatic organisms. The salinity based zonation during pre-Farakka period apparently stands modified with a downward shift of freshwater zone. Accordingly, distribution and abundance of biotic communities like plankton and fish now present a completely different scenario from the past.

Examining Seasonally Pulsed Detrital Transport in the Coastal Everglades Using a Sediment Tracing Technique

The Comprehensive Everglades Restoration includes plans to restore freshwater delivery to Taylor Slough, a shallow drainage basin in the Southern Everglades, ultimately resulting in increased freshwater flow to the downstream Taylor River estuary. The effect of altered hydrologic regime on the transport dynamics of flocculent, estuarine detritus is not well understood. We utilized a paramagnetic sediment tracer to examine detrital transport in three Taylor River pond/creek pairs during early wet versus late wet transition season estuarine flow conditions. Flux of floc tracer was greatest in the downstream direction during all observations, and was most pronounced during the early wet season, coincident with shallower water depth and faster discharge from northern Taylor River. Floc tracer was more likely to move upriver during the late wet/dry season. We observed a floc tracer transport velocity of approximately 1.74 to 1.78 m/day across both seasonal hydrologic conditions. Tracer dynamics were also surprisingly site-dependent, which may highlight the importance of channel geomorphology in regulating hydrologic and sediment transport conditions. Our data suggest that restoration of surface water delivery to Taylor River will influence downstream loading of detritus material into riverine ponds. These detrital inputs have the potential to enhance ecosystem primary productivity and/or secondary productivity.

Assessment of pressures and impacts on surface water bodies of the Mediterranean. Case study: Pamvotis Lake, Greece

The aim of the study presented in this article is to assess the ecological status of a surface water body in the Mediterranean using the methodological approach of Driver-Pressure-State-Impact-Response. Based on this approach for the case study analyzed (Pamvotis Lake, Greece), it is concluded that the main drivers, which lead to pressures in the study area are: intensive agricultural activities, alteration of hydrological regime, contamination from point sources and changes in the land-use and fish stocking. The ecological status is assessed by analysing data series of physical, chemical and biological elements that are available from early ’80s. Findings suggest elevated nutrient concentrations sufficient for maintaining eutrophic conditions while their seasonal variability is mostly driven by factors as water level fluctuation, catchment runoff and in-lake biological processes. Subsequently, concerning biotic factors, the poor biodiversity mainly represented by the dominance of the most tolerant species, confirm the previous profile. Since, reference conditions have only recently been established in Greece, the ECOFRAME scheme and the guidelines proposed by the “Intercalibration Group for Mediterranean Lakes” were applied. In terms of the above elements; the water quality status could be characterized as “High”, “High to Good” and “High to Bad”, respectively, whereas the overall ecological status tends to shift in poor conditions. Finally, the major response actions needed should be in the direction of reduced application of fertilizers and chemicals in the cultivated land of the catchment, removal of the point-contamination sources from the catchment, appropriate land-use management and biomanipulation.

Climate change threatens coexistence within communities of Mediterranean forested wetlands.

The Mediterranean region is one of the hot spots of climate change. This study aims at understanding what are the conditions sustaining tree diversity in Mediterranean wet forests under future scenarios of altered hydrological regimes. The core of the work is a quantitative, dynamic model describing the coexistence of different Mediterranean tree species, typical of arid or semi-arid wetlands. Two kind of species, i.e. Hygrophilous (drought sensitive, flood resistant) and Non-hygrophilous (drought resistant, flood sensitive), are broadly defined according to the distinct adaptive strategies of trees against water stress of summer drought and winter flooding. We argue that at intermediate levels of water supply the dual role of water (resource and stress) results in the coexistence of the two kind of species. A bifurcation analysis allows us to assess the effects of climate change on the coexistence of the two species in order to highlight the impacts of predicted climate scenarios on tree diversity. Specifically, the model has been applied to Mediterranean coastal swamp forests of Central Italy located at Castelporziano Estate and Circeo National Park. Our results show that there are distinct rainfall thresholds beyond which stable coexistence becomes impossible. Regional climatic projections show that the lower rainfall threshold may be approached or crossed during the XXI century, calling for an urgent adaptation and mitigation response to prevent biodiversity losses.

Aquatic plant dynamics of Waituna Lagoon, New Zealand: trade-offs in managing opening events of a Ramsar site

Coastal lagoons are at risk internationally due to impacts associated with human-induced land use change. The resilience of aquatic macrophytes in these systems is threatened by altered hydrological regimes, elevated nutrient loading, and increased dominance of nuisance species. We describe the aquatic plant dynamics of the Waituna Lagoon Ramsar Site, a 1,350 ha lagoon frequently opened to the sea for flood mitigation which is characterised by fluctuating water levels and salinity. The shallow lagoon supports a macrophyte community dominated by Ruppia megacarpa and R. polycarpa. Repeated survey of 48 sites across the lagoon during late summer in 2009, 2010 and 2011 were applied to describe aquatic plant composition and abundance. This period coincided with three opening events (winter 2008; winter 2009; spring 2010) when the lagoon switched from a predominantly fresh-brackish system to being influenced by tidal exchange and lower water levels. The lagoon experienced a period of 43 days open to the sea in 2008–2009, 67 days in 2009–2010 and 181 days in 2010–2011, during which macrophytes were subject to saline conditions in excess of 10 ppt. We observed a decline in the occurrence of Ruppia from 2009 (69 % sites) to 2011 (23 % sites). The shift in productivity was associated with the duration of the open phase and the period plants were subject to saline conditions >20 ppt and low water levels. The resilience of the system is also at risk from increased algal-dominance due to the intensification of agricultural land use occurring in the Waituna Lagoon catchment. While lagoon opening events cause extreme changes in water depth and salinity that can limit macrophyte growth, they also provide a mechanism to reduce the effects of eutrophication. Understanding these trade-offs is pivotal in management decisions regarding the likely impact of opening events on the ecological character of coastal lagoons.

Damming the prairie: Human alteration of Great Plains river regimes

Many studies have investigated post-impoundment hydrologic regime alteration; however, the Great Plains of the United States are often excluded from these analyses. The goal of this analysis was to evaluate the pre and post-impact hydrologic regimes of Great Plains rivers. The hydrologic records of nine large rivers were analyzed to quantify the magnitude, duration, and direction of hydrologic alteration attributable to impoundment. An additional tenth system, the Red River of the North, was included in the analysis to provide an example of a comparable regional hydrologic regime without the presence of impoundments on the main-stem of the network. Hydrologic regimes were analyzed using the Indicators of Hydrologic Alteration, a model that estimates 33 hydrologic and ecologically relevant parameters. For many of the parameters, the magnitude, duration, and direction were similar across the systems. The results showed a significant increase in the 1 through 90 day minimum discharges and a significant decrease in the 1 through 90 day maximum discharge; though the magnitude of alteration decreased with increased temporal averaging. The most dramatic alterations were large increases in the number of annual hydrograph reversals and faster rise and fall rates. Results of this study are the first to quantify the widespread hydrologic alteration of Great Plains rivers following impoundment.

Adapting the operation of two cascaded reservoirs for ecological flow requirement of a de-watered river channel due to diversion-type hydropower stations

Alteration of hydrological regime due to reservoir operation has significant impacts on the river ecosystem, in particular for diversion-type hydropower stations that make part of the natural river channel considerably de-watered. Maintaining ecological flow is considered an effective way to remediate the damages. However, it may jeopardize the socio-economic benefit of reservoirs, for example reduction of power production. The conflicting objectives bring a dilemma to water managers in defining the reservoir operation policy. This study considers two cascaded reservoirs in the Yalong River, and develops an optimization model to explore trade-offs between hydropower generation and ecological flow requirement. The objective function of the model is the total power production. In addition to conventional constraints on the water level and discharge, the model takes into account downstream ecological flow requirement, defined as a hydrograph representing the daily flow requirement to conserve the habitats of the indigenous fish Schizothorax chongi (S. chongi). The optimization model allows establishing a relation between the target of fish habitat conservation and the corresponding loss of hydropower production, so as to propose compromise solutions. Although the model has only been applied in the paper to one case study, its generic formulation allows applying it to a broad range of cascaded reservoir configurations. Moreover, extensions towards cases with ecological flow requirements for more than one species are straightforward.

Refuge habitats for fishes during seasonal drying in an intermittent stream: movement, survival and abundance of three minnow species

Drought and summer drying can be important disturbance events in many small streams leading to intermittent or isolated habitats. We examined what habitats act as refuges for fishes during summer drying, hypothesizing that pools would act as refuge habitats. We predicted that during drying fish would show directional movement into pools from riffle habitats, survival rates would be greater in pools than in riffles, and fish abundance would increase in pool habitats. We examined movement, survival and abundance of three minnow species, bigeye shiner (Notropis boops), highland stoneroller (Campostoma spadiceum) and creek chub (Semotilus atromaculatus), during seasonal stream drying in an Ozark stream using a closed robust multi-strata mark-recapture sampling. Population parameters were estimated using plausible models within program MARK, where a priori models are ranked using Akaike’s Information Criterion. Creek chub showed directional movement into pools and increased survival and abundance in pools during drying. Highland stonerollers showed strong directional movement into pools and abundance increased in pools during drying, but survival rates were not significantly greater in pools than riffles. Bigeye shiners showed high movement rates during drying, but the movement was non-directional, and survival rates were greater in riffles than pools. Therefore, creek chub supported our hypothesis and pools appear to act as refuge habitats for this species, whereas highland stonerollers partly supported the hypothesis and bigeye shiners did not support the pool refuge hypothesis. Refuge habitats during drying are species dependent. An urgent need exists to further understand refuge habitats in streams given projected changes in climate and continued alteration of hydrological regimes.

Seasonal and Annual Impacts of Climate Change on Watershed Response Using an Ensemble of Global Climate Models

Climate change impacts watershed hydrology and contributes to alteration of hydrologic regimes in streams. However, global climate models (GCMs) operate at spatial and temporal scales that are too large to capture important watershed-scale hydrologic shifts. A method of disaggregating monthly ensemble GCM data into temperature and precipitation data series for daily, watershed-specific hydrologic simulations with SWAT was developed and assessed in the Soldier Creek watershed in northeast Kansas. A stochastic weather generator (WINDS) was employed to produce a baseline scenario (no changes from late 20th century conditions) and two scenarios based on ensemble means of 15 GCMs representing future conditions (A2 storyline) referred to as the 2050 and 2100 scenarios. Future hydrologic regimes exhibited non-linear annual and monthly responses in hydrologic budget components, such as surface runoff, baseflow, and soil moisture, to temperature and precipitation changes. For the 2050 scenario, the combination of higher temperatures along with decreased annual precipitation and increased spring precipitation resulted in higher surface runoff, baseflow, and streamflow in May and June with a longer drought season later in summer. The significant decrease in streamflow, runoff, and baseflow for the 2100 scenario reflected an increase in monthly and annual temperature rather than a direct result of precipitation decline. The 2100 scenario also produced a reduction in low-flow duration, an increase in the number of drought occurrences, and a decrease in flood frequency and duration. In retrospect, use of the stochastic weather generator to temporally downscale monthly GCM results while incorporating site-specific climate variability (such as occurs with convective storms often missed in coarse-resolution GCM data) produced more meaningful analysis of hydrological impacts, which is critical to predicting and understanding the impacts of climate change. Although this method allowed simulation of future-climate shifts based on GCM-simulated monthly shifts, it could not simulate potential shifts in climate patterns within a month, such as changes in transitional probabilities that govern the intensity and distribution of storms with months. In future work, translation of regional climate model responses into WINDS stochastic parameter adjustments will allow more accurate and efficient simulation. The severity of the increased drought and decreased flood responses simulated in this study would not be anticipated by review of precipitation trends alone nor by analysis of annual hydrologic responses alone. Similarly, many critical hydrologic responses reflected interactions between climate variables (e.g., precipitation and temperature) at sub-annual temporal scales, which highlights the need to consider climatic interactions in future studies of climate change impacts.

Assessment of methane and nitrous oxide fluxes in rural landscapes

We estimated CH 4 and N 2O emissions from the main land-use types in rural landscapes using data from the literature (950 study sites/experiments from the temperate and boreal zone published from 1980 to 2009 in 165 scientific papers indexed by the ISI Web of Science) and assessed the emission potential of CH 4 and N 2O from rural landscapes in Estonia. According to this analysis, natural peatlands and marshes appeared to be the most important CH 4 emitters, whereas N 2O is emitted mainly from drained peatlands and marshes, set aside areas, conventional arable lands, fertilized grasslands, and coniferous and mixed forests – all on hydromorphic soils. The estimated median value of annual CH 4-C and N 2O-N fluxes for Estonian rural landscapes are 25,519 and 11,050 t respectively. CH 4 consumption makes up 13.2% of the emission. The largest CH 4 emitters are peatlands (17,746 t CH 4-C year −1; 60%), whereas coniferous and mixed forests on hydromorphic soils with altered hydrologic regime are responsible for the bulk (51%) of N 2O fluxes. The Global Warming Potential (GWP) of Estonian rural land-use types (42,685 km 2) from potential CH 4 and N 2O fluxes is 5.99 million t of CO 2 equivalents, of which N 2O is responsible for 86%. Several measures for the further mitigation of greenhouse gas emission from rural landscapes are proposed.

Spread and impact of introduced conifers in South America: Lessons from other southern hemisphere regions

AbstractThe history of conifers introduced earlier elsewhere in the southern hemisphere suggests that recent invasions in Argentina, Brazil, Chile and Uruguay are likely to increase in number and size. In South Africa, New Zealand and Australia, early ornamental introductions and small forestry plantations did not lead to large‐scale invasions, while subsequent large plantations were followed with a lag of about 20–30 years by troublesome invasions. Large‐scale conifer plantation forestry in South America began about 50–80 years later than in South Africa, Australia and New Zealand, while reports of invasions in South America lagged behind those in the latter nations by a century. Impacts of invading non‐native conifers outside South America are varied and include replacement of grassland and shrubland by conifer forest, alteration of fire and hydrological regimes, modification of soil nutrients, and changes in aboveground and belowground biotic communities. Several of these effects have already been detected in various parts of South America undergoing conifer invasion. The sheer amount of area planted in conifers is already very large in Chile and growing rapidly in Argentina and Brazil. This mass of reproductive trees, in turn, produces an enormous propagule pressure that may accelerate ongoing invasions and spark new ones at an increasing rate. Regulations to control conifer invasions, including measures to mitigate spread, were belatedly implemented in New Zealand and South Africa, as well as in certain Australian states, inspired by observations on invasions in those nations. Regulations in South America are weaker and piecemeal, but the existing research base on conifer invasions elsewhere could be useful in fashioning effective regulations in South America. Pressure from foreign customers in South Africa has led most companies there to seek certification through the Forestry Stewardship Council; a similar programme operates in Australia. Such an approach may be promising in South America.

Composition and relative health of remnant vegetation fringing lakes along a salinity and waterlogging gradient

Extensive land clearing for agriculture in south-west Western Australia has led to highly fragmented patches of remnant vegetation. In this landscape, the fringing vegetation of lakes has an important conservation priority in a biologically diverse region but is vulnerable to altered hydrological regimes and easily degraded by waterlogging and salinity. Protection of the fringing vegetation with direct intervention approaches such as drainage or pumping schemes requires knowledge of the tolerance or ‘coping’ range of species targeted for conservation. To obtain this information the health of vegetation in relation to waterlogging and salinity is assessed in two lake systems north of Esperance in south-western Australia. The lower reaches of both systems are dominated by healthy halophytic species. Mesophytes, phreatophytes, xerophytes, and combinations of these classes dominate the upper reaches but are mostly degraded. There are unhealthy and healthy pockets of mesophytic, phreatophytic, xerophytic species, and combinations of these classes occurring at similar elevations above shallow groundwater, indicating that temporal hydroperiod thresholds are important for these species.

Implication of nutrient and salinity interaction on the productivity of Spartina patens

Reintroduction of fresh water to coastal systems with altered hydrologic regimes is a management option for restoring degraded wetland habitats. Plant production in these systems is believed to be enhanced by increased nutrient availability and reduced salinity. Although studies have documented nutrient limitation and salinity stress in coastal marshes, interpreting the effects of freshwater reintroduction on plant production is difficult because high nutrient availability often is confounded with low salinity. We tested the hypothesis that plant growth response to nutrients does not vary with salinity in a greenhouse study. Treatments consisted of four nutrient concentrations and four non-lethal salinity levels; plant response was measured as biomass accumulation after 144 days of exposure. The significant interaction between salinity and nutrient concentrations indicates that response of Spartina patens marshes to freshwater inflows would vary by site-specific soil conditions. Biomass decreased with increased salinity at all four nutrient concentrations with variation among the nutrient concentrations decreasing as salinity increased. We demonstrate the importance of considering ambient salinity and nutrient soil conditions in restoration planning involving freshwater inflow. We propose salinity should remain a primary concern in restoration plans targeted at improving degraded S. patens-dominated marsh habitat.

POSSIBILITIES TO RESTORE NATURAL WATER REGIME IN THE ŽUVINTAS LAKE AND SURROUNDING WETLANDS ‐ MODELLING ANALYSIS APPROACH/NATŪRALAUS VANDENS REŽIMO ŽUVINTO EŽERE IR APLINKINĖSE PELKĖSE ATKŪRIMO ANALIZĖ TAIKANT MATEMATINĮ MODELIAVIMĄ/ AНAЛИЗ ВОССТАНОВЛЕНИЯ ВОДНОГО РЕЖИМА В ОЗЕРЕ ЖУВИНТАС И ОКРУЖАЮЩИХ БОЛОТАХ С ПОМОЩЬЮ МЕТОДА МАТЕМАТИЧЕСКОГО МОДЕЛИРОВАНИЯ

The Žuvintas Lake, located in southern Lithuania in the basin of the Dovine River is one of the biggest lakes and the oldest natural reserves of the country. However, the changes in the hydrology of the Dovine River basin, caused by large‐scale melioration and water management works carried out in the 20th century, have resulted in significant alteration of hydrological regime and decrease in biodiversity of the Žuvintas Lake and surrounding wetlands. In order to prevent the ongoing deterioration of the Lake and wetlands solutions have to be found. Therefore, various scenarios have been analysed to evaluate the impact of water management alternatives. For these scenarios the physically‐based distributed parameter model SIMGRO was used. The results have shown that natural water regime in the Žuvintas Lake is hardly reversible. However, the replacement of sluice‐gates implemented at the outlet of the Žuvintas Lake by overflow weir as well as the blocking of drainage ditches and the removal of scrubs and trees in the wetlands surrounding the Lake can be highly successful measures to improve hydrological conditions. Santrauka Dovinės upės (dešinysis Šešupės upės intakas) baseine yra seniausias Lietuvoje Žuvinto biosferos rezervatas ir kitos europinės svarbos saugomos teritorijos. Tose vietose hidrologinis režimas tiesiogiai reguliuojamas šešiose vietose pastatytais reguliavimo šliuzais. Šiuo metu poreikio reguliuoti nėra, todėl darbe analizuojamos natūralaus vandens režimo atkūrimo galimybės Žuvinto ežere ir aplinkinėse pelkėse. Tam buvo taikytas matematinio modeliavimo metodas naudojant pasiskirsčiusių parametrų SIMGRO modelį. Ankstesni tyrimai parodė, kad atkurti natūralų hidrologinį režimą vien panaikinus reguliavimo šliuzą žemiau Žuvinto ežero, negalima. Tai sunaikintų ežerą ir neigiamai paveiktų požeminio vandens režimą Žuvinto ir Amalvos pelkių komplekse. Siekiant bent dalinio vandens režimo natūralizavimo reguliavimo šliuzą siūloma rekonstruoti į slenkstinę nuopylą įrengiant žuvitakį. Žuvinto ir Amalvos pelkių masyve požeminio vandens režimui pagerinti rekomenduojama pašalinti ten augančią sumedėjusią augaliją ir apypelkio teritorijose patvenkti melioracijos griovius. Pateikiamas tokių priemonių galimas poveikis Žuvinto ežero ir aplinkinių pelkių hidrologiniam režimui. Peзюме Водный режим бассейнa реки Довине в южной части Литвы в прошлом столетии был подвержен важным изменениям. Там находится старый заповедник Литвы – озеро Жувинтас c близлежащими болотaми. В статье представлен сценарий по восстановлению водного режима в озере Жувинтас и окружающих болотах. Для исследования была применена математическая модель SIMGRO. Результаты показали, что полное восстановление гидрологического режима в озере невозможно. Для улучшения водного режима предложен ряд мер.

Ecological consequences of altered hydrological regimes in fragmented ecosystems in southern Australia: Impacts and possible management responses

Ecological consequences of altered hydrological regimes in fragmented ecosystems in southern Australia: Impacts and possible management responses

Benthic macroinvertebrates as indicators of biological condition below hydropower dams on west slope Sierra Nevada streams, California, USA

AbstractOver 50 hydropower dams in California will undergo relicensing by the Federal Energy Regulatory Commission (FERC) in the next 15 years. An interpretive framework for biological data collected by relicensing studies is lacking. This study developed a multi‐metric index of biotic integrity (IBI) to assess biological condition below hydropower diversion dams on west slope Sierra Nevada streams based on benthic macroinvertebrates (BMIs). Ten streams were sampled above the upstream influence of peak reservoir storage and at five downstream sites sequentially spaced 500 m apart. Reference conditions were defined by screening upstream study sites and 77 other regional streams using quantitative GIS land use analysis, reach‐scale physical habitat (PHAB) data and water chemistry data. Eighty‐two metrics were evaluated for inclusion in the IBI based on three criteria: (1) good discrimination between reference and first downstream sites with some indication of recovery over the distance sampled; (2) sufficient range for scoring; (3) minimal correlation with other discriminating metrics. The IBI showed good discrimination between reference and downstream sites with partial recovery as distance downstream increased, and was validated with an independent dataset. Individual metrics, IBI scores and multivariate ordination axes were poorly correlated with PHAB variables across sites. When only reference and first downstream sites were evaluated, decreased IBI scores were related to lower habitat variability and substrate coarsening below dams. Lower IBI scores below dams were most strongly associated with altered hydrologic regime, especially non‐fluctuating flows as defined by the flow constancy/predictability index. Flow restoration experiments would be valuable in developing management actions that achieve a sustainable balance between conflicting human and ecological needs for freshwater. Copyright © 2008 John Wiley & Sons, Ltd.