Biological Responses to Contrasting Hydrology in Backwaters of Upper Mississippi River Navigation Pool 25

Water level management in Mississippi River Pool 25 differentially influences off-channel habitats in the mid-pool and lower pool. Hydrologic models indicate lower pool off-channel habitats dry with greater frequency and duration compared to similar habitats at mid-pool. We examined the influence of this contrasting hydrology on substrate characteristics, organic matter, macroinvertebrate, and fish communities in off-channel habitats during 2001–2003. Benthic organic matter standing stocks were stable in mid-pool habitats but lower pool values were variable because of annual differences in moist-soil vegetation production. Generally, small-bodied and multivoltine invertebrate taxa had high community biomass and dominated lower pool habitats, whereas longer-lived and large-bodied taxa were more abundant and had higher community biomass in mid-pool habitats having longer hydroperiods. Fish communities were dominated by cyprinids in both habitats, and mid-pool habitats tended to be higher in overall species richness. Unique fish taxa were collected in each pool, with primarily rheophilic forms in mid-pool habitats and limnophilic forms in lower pool habitats. Results indicate that contrasting hydrology associated with a mid-pool control point directly and indirectly influences biological communities in off-channel habitats. Further, management regimes that promote hydrologic diversity in off-channel habitats may enhance biological diversity at larger spatial and temporal scales.     

Minimal models and agroecological policy at the regional scale: An application to salinity problems in southeastern Australia

A minimal dynamical systems model that couples agricultural activity, native vegetation, and hydrological processes is developed to explore policy options regarding regional-scale soil and water salinization in southeastern Australia. The analysis suggests that although considerable revegetation is required to restore catchment water balance, the current value of water in uses other than agriculture is too low for revegetation to be economically viable. In contrast, groundwater pumping generates significant short-term gains by preventing soil salinization but is not a viable long-term solution. Thus, effective salinity management policy must include mechanisms to increase the value of water in uses other than irrigated agriculture to achieve sufficient long-term revegetation. These results are robust over a wide range of parameter values and thus provide a basis for policy action in the face of uncertainty about groundwater flow characteristics.     

The Environmental Capacity Approach to the Control of Marine Pollution: The Case of Copper in the Krka River Estuary

Changes in soil pH, soil heavy metal forms, and the metabolic diversity of microbial communities were examined in soil samples collected in 1-mm increments from barley roots in soil contaminated with cadmium (Cd) and zinc (Zn) using a rhizobox system. Concentrations of exchangeable Cd and Zn increased near the roots owing to a decrease in soil pH. Conversely, the concentration of inorganically bound Cd and Zn decreased near the roots. Despite having the highest concentration of the most toxic exchangeable metals, the rhizosphere also had the highest bacterial and fungal metabolic activity and diversity when assessed using BIOLOG plates. Therefore, the promoting effects of root exudates on microbial activity could outweigh the adverse effects of Cd and Zn on microorganisms in the rhizosphere.     

Basic Principles and Ecological Consequences of Altered Flow Regimes for Aquatic Biodiversity

The flow regime is regarded by many aquatic ecologists to be the key driver of river and floodplain wetland ecosystems. We have focused this literature review around four key principles to highlight the important mechanisms that link hydrology and aquatic biodiversity and to illustrate the consequent impacts of altered flow regimes: Firstly, flow is a major determinant of physical habitat in streams, which in turn is a major determinant of biotic composition; Secondly, aquatic species have evolved life history strategies primarily in direct response to the natural flow regimes; Thirdly, maintenance of natural patterns of longitudinal and lateral connectivity is essential to the viability of populations of many riverine species; Finally, the invasion and success of exotic and introduced species in rivers is facilitated by the alteration of flow regimes. The impacts of flow change are manifest across broad taxonomic groups including riverine plants, invertebrates, and fish. Despite growing recognition of these relationships, ecologists still struggle to predict and quantify biotic responses to altered flow regimes. One obvious difficulty is the ability to distinguish the direct effects of modified flow regimes from impacts associated with land-use change that often accompanies water resource development. Currently, evidence about how rivers function in relation to flow regime and the flows that aquatic organisms need exists largely as a series of untested hypotheses. To overcome these problems, aquatic science needs to move quickly into a manipulative or experimental phase, preferably with the aims of restoration and measuring ecosystem response.     

Climate and land-use changes affecting river sediment and brown trout in alpine countries—a review

Background, aim, and scope

Catch decline of freshwater fish has been recorded in several countries. Among the possible causes, habitat change is discussed. This article focuses on potentially increased levels of fine sediments going to rivers and their effects on gravel-spawning brown trout. Indications of increased erosion rates are evident from land-use change in agriculture, changes in forest management practices, and from climate change. The latter induces an increase in air and river water temperatures, reduction in permafrost, changes in snow dynamics and an increase in heavy rain events. As a result, an increase in river sediment is likely. Suspended sediment may affect fish health and behaviour directly. Furthermore, sediment loads may clog gravel beds impeding fish such as brown trout from spawning and reducing recruitment rates. To assess the potential impact on fine sediments, knowledge of brown trout reproductive needs and the effects of sediment on brown trout health were evaluated.

Approach

We critically reviewed the literature and included results from ongoing studies to answer the following questions, focusing on recent decades and rivers in alpine countries.

Have climate change and land-use change increased erosion and sediment loads in rivers?

Do we have indications of an increase in riverbed clogging?

Are there indications of direct or indirect effects on brown trout from increased suspended sediment concentrations in rivers or from an increase in riverbed clogging?

Results

Rising air temperatures have led to more intensive precipitation in winter months, earlier snow melt in spring, and rising snow lines and hence to increased erosion. Intensification of land use has supported erosion in lowland and pre-alpine areas in the second half of the twentieth century. In the Alps, however, reforestation of abandoned land at high altitudes might reduce the erosion risk while intensification on the lower, more easily accessible slopes increases erosion risk. Data from laboratory experiments show that suspended sediments affect the health and behaviour of fish when available in high amounts. Point measurements in large rivers indicate no common lethal threat and suspended sediment is rarely measured continuously in small rivers. However, effects on fish can be expected under environmentally relevant conditions. River bed clogging impairs the reproductive performance of gravel-spawning fish.

Discussion

Overall, higher erosion and increased levels of fine sediment going into rivers are expected in future. Additionally, sediment loads in rivers are suspected to have considerably impaired gravel bed structure and brown trout spawning is impeded. Timing of discharge is put forward and is now more likely to affect brown trout spawning than in previous decades.

Conclusions

Reports on riverbed clogging from changes in erosion and fine sediment deposition patterns, caused by climate change and land-use change are rare. This review identifies both a risk of increases in climate erosive forces and fine sediment loads in rivers of alpine countries. Increased river discharge and sediment loads in winter and early spring could be especially harmful for brown trout reproduction and development of young life stages. Recently published studies indicate a decline in trout reproduction from riverbed clogging in many rivers in lowlands and alpine regions. However, the multitude of factors in natural complex ecosystems makes it difficult to address a single causative factor.

Recommendations and perspectives

Further investigations into the consequences of climate change and land-use change on river systems are needed. Small rivers, of high importance for the recruitment of gravel-spawning fish, are often neglected. Studies on river bed clogging are rare and the few existing studies are not comparable. Thus, there is a strong need for the development of methods to assess sediment input and river bed clogging. As well, studies on the effects to fish from suspended sediments and consequences of gravel beds clogging under natural conditions are urgently needed.     

Isolated Spring Wetlands in the Great Basin and Mojave Deserts,USA: Potential Response of Vegetation to Groundwater Withdrawal

Desert springs, often the sole sources of water for wildlife and cattle, support wetland and wetland/upland transition ecosystems including rare and endemic species. In the basin and range province in Nevada, USA, springs in the Great Basin and Mojave deserts are sustained by interconnected deep carbonate and shallow basin-fill aquifers which are threatened by proposed groundwater withdrawal to sustain rapidly expanding urban areas, a common problem in arid regions worldwide. This paper draws on historic groundwater data, groundwater modeling, and studies of environmental controls of spring ecosystems to speculate on the potential effects of groundwater withdrawal and water table decline on spring-supported vegetation. The focus is on springs in the Great Basin and Mojave deserts representative of those that may be affected by future, planned groundwater withdrawal. Groundwater withdrawal is expected to reduce spring discharge directly through reduced flows from the shallow basin-fill aquifer or through reduction of the hydraulic head of the deep carbonate aquifer. This flow reduction will truncate the outflow stream, reducing the areal cover of wetland and wetland/upland transition vegetation. Lowering the local water table may also reduce the amount of upland phreatophytic vegetation by causing water levels to drop below plant rooting depths. Percolation of salts to surface soils may be reduced, eventually altering desert shrub cover from halophytes to nonhalophytes. The extent of these effects will vary among springs, based on their distance from extraction sites and location relative to regional groundwater flow paths. On-site monitoring of biotic variables (including cover of selected hygrophytes and phreatophytes) should be a necessary complement to the planned monitoring of local hydrologic conditions.     

Assessing Watershed-Scale, Long-Term Hydrologic Impacts of Land-Use Change Using a GIS-NPS Model

Land-use change, dominated by an increase in urban/impervious areas, has a significant impact on water resources. This includes impacts on nonpoint source (NPS) pollution, which is the leading cause of degraded water quality in the United States. Traditional hydrologic models focus on estimating peak discharges and NPS pollution from high-magnitude, episodic storms and successfully address short-term, local-scale surface water management issues. However, runoff from small, low-frequency storms dominates long-term hydrologic impacts, and existing hydrologic models are usually of limited use in assessing the long-term impacts of land-use change. A long-term hydrologic impact assessment (L-THIA) model has been developed using the curve number (CN) method. Long-term climatic records are used in combination with soils and land-use information to calculate average annual runoff and NPS pollution at a watershed scale. The model is linked to a geographic information system (GIS) for convenient generation and management of model input and output data, and advanced visualization of model results. The L-THIA/NPS GIS model was applied to the Little Eagle Creek (LEC) watershed near Indianapolis, Indiana, USA. Historical land-use scenarios for 1973, 1984, and 1991 were analyzed to track land-use change in the watershed and to assess impacts on annual average runoff and NPS pollution from the watershed and its five subbasins. For the entire watershed between 1973 and 1991, an 18% increase in urban or impervious areas resulted in an estimated 80% increase in annual average runoff volume and estimated increases of more than 50% in annual average loads for lead, copper, and zinc. Estimated nutrient (nitrogen and phosphorus) loads decreased by 15% mainly because of loss of agricultural areas. The L-THIA/NPS GIS model is a powerful tool for identifying environmentally sensitive areas in terms of NPS pollution potential and for evaluating alternative land use scenarios for NPS pollution management.     

A comparison of tools for modeling freshwater ecosystem services

Interest in ecosystem services has grown tremendously among a wide range of sectors, including government agencies, NGO’s and the business community. Ecosystem services entailing freshwater (e.g. flood control, the provision of hydropower, and water supply), as well as carbon storage and sequestration, have received the greatest attention in both scientific and on-the-ground applications. Given the newness of the field and the variety of tools for predicting water-based services, it is difficult to know which tools to use for different questions. There are two types of freshwater-related tools – traditional hydrologic tools and newer ecosystem services tools. Here we review two of the most prominent tools of each type and their possible applications. In particular, we compare the data requirements, ease of use, questions addressed, and interpretability of results among the models. We discuss the strengths, challenges and most appropriate applications of the different models. Traditional hydrological tools provide more detail whereas ecosystem services tools tend to be more accessible to non-experts and can provide a good general picture of these ecosystem services. We also suggest gaps in the modeling toolbox that would provide the greatest advances by improving existing tools.     

Changes in river discharge structure and regime in mining-industrial-urban areas

In mining-industrial-urban areas, the variability of river discharge is regulated, directly or indirectly, by human economic activity. This results from the presence of alien water, which often comes from outside the catchment area, is discharged into the river network. This water includes industrial and municipal wastewater and deep-drainage mine water. Simultaneously, as a result of water intake and water infiltration into dry ground (due to mining), the volume of river discharge decreases. Such changeable conditions of water alimentation and drainage are typical of many regions of Europe. Detailed investigations of the range and directions of changes in river structure and regime were carried out for the area of Upper Silesian Industrial Region (USIR) of Poland. The results were compared with the results of investigations carried out in the Ruhr Basin of Germany and the Donetsk Basin of the Ukraine and Russia. The investigations showed that, in some cases, prolonged, multifunctional economic activity of a man has effectively eliminated of the influence of natural hydrometeorological conditions on river discharge. Wastewater and mine water which has contributed to river flow is only slightly variable in the annual cycle and it causes an increase of water volume and a discharge smoothing. Sewage effluent and mine wastewater also change the structure of river runoff because their contribution to the runoff sometimes exceeds 90% of its volume.     

Coping with changing water resources: The case of the Syr Darya river basin in Central Asia

This paper discusses how climatic-hydrological and socio-political developments will affect water allocation in the Syr Darya river basin and which adaptation measures will be needed to cope with changing water resources. In view of the geo-political complexity, climate-driven changes in water availability are of particular importance in this region. Water shortages during summer will become more frequent as precipitation is expected to further decrease and glacial meltwater releases will decrease in the long-term due to reduced glacier volume. Being the main valve to the entire Syr Darya river system, the Toktogul reservoir in Kyrgyzstan could take over, at least partly, the role of glaciers as seasonal water redistributors, thus allowing the generation of energy in winter – benefiting upstream countries – and irrigation for large-scale agriculture in summer – benefiting downstream countries. To date, however, there is no regional consensus on a balanced reservoir management, which currently favours irrigation according to past Soviet priorities. Moreover, the perception of water as a ‘national concern’ in Central Asia discourages efforts towards cooperation between states at the regional level. So far, climate change adaptation has focused on technical rather than institutional solutions. We suggest that policy-relevant adaptation measures should include consistent data collection and dissemination, cross-sectoral collaboration, promotion of national responsibility and initiative, and agreeing on a regional strategy.