Lakes and Reservoirs: Research and Management

This work investigates the effects of climate and hydrology as factors controlling the trophic status of Sélingué, a monomictic reservoir in Mali, West Africa. Environmental (water transparency, hydrochemistry, nutrients) and biological (chlorophyll a concentrations) descriptors were studied on water samples collected biweekly from November 2000 to November 2001 in a station representative of the northern part of the water body. Statistical methods were used to estimate the existence and significance of breaks in the time series and environmental data were used to explain these breaks. In Sélingué Reservoir, the water column is stratified from March to May as a result of the cooling induced by the harmattan (North‐East trade winds). Stratification lasts a few weeks, until the beginning of the monsoon (South‐West trade winds), after which progressive warming allows vertical mixing of the lake. In harmattan or monsoon situations, the winds do not play a significant role except for storm events during the rainy season. Such events can change transiently, but markedly, the physical conditions prevailing in the whole water column. The water quality closely follows the hydrological cycle, characterized by a unique flood, which lasts a few weeks, from mid‐July. Input of nutrients during the flood events is limited and local mineralization of organic matter in the hypolimnion during the stratification period seems to play a major role in the availability of dissolved inorganic nitrogen and soluble reactive phosphorus. This availability is subject to vertical mixing which is only possible when the water height is sufficiently low and the wind‐induced energy is sufficiently high. Dry (dust during the harmattan period) and wet deposition (linked to rains) play a role in supplying nutrients to the lake and can be factors in the observed increased chlorophyll a concentrations. Thus, environmental factors in Sélingué change with the current hydrological conditions. Sélingué Reservoir can be regarded as oligotrophic during the high water period, but as meso‐eutrophic during the low water period. Each annual flood initializes the ecological conditions in this water body. This pattern limits the risks of trophic change (which can lead to algal blooms) to short periods of very low water levels immediately preceding flood events.

This study introduces the emerging integrated ecosystem management approach known as Payments for Watershed Services (PWS) as utilized for lake and reservoir basin governance. PWS is built on the central concept of providing economic incentives to watershed stakeholders to assist in management efforts. It channels conservation payments from downstream payers to finance conservation activities conducted by upstream payees. The upstream conservation activities are expected to enhance ecosystem functions, thereby improving water‐related ecosystem services desired by downstream stakeholders. Information on 163 PWS projects in 34 developing countries through the year 2008 was collected and analysed, including their common goals, processes, outcomes, scientific assumptions and socioeconomic rationales. This study recognized one unique PWS characteristic, namely the role of intermediary organizations (i.e. brokers) in integrating the economic incentives of upstream payees and downstream payers in order to facilitate their transactions by means of contracts. Although 75% of the reviewed PWS projects have focused on rivers, and only 10% have considered lakes and reservoirs, the similarity of the intermediary functions performed by lake management organizations and PWS intermediary organizations suggests a greater potential for the future application of PWS designs in lake basins. Drawing on components in the field of New Institutional Economics to interpret the intermediary function within the PWS framework, a three‐part PWS design with 15 steps is proposed in this study for lake basin governance, with a Costa Rican PWS scheme serving as an illustration. This study seeks to communicate the scientific and socioeconomic frontiers for developing locally suitable and integrated watershed governance structures to lake management organizations and other watershed stakeholder groups.

Intermediate host snails of schistosomiasis were surveyed in this study to determine their abundance and distribution in the lake and land aquatic habitats of Lake Victoria basin of Kenya. Several sites were sampled at eight locations, both in the lake and on the land. The habitat and/or vegetation type (i.e. open water, hippo grass, hyacinth, ambatch trees, other vegetation, stream, swamp, pond, dam) of the sampled aquatic sites within the locations were also differentiated, water physicochemical parameters were determined, and the abundance of different species or taxa of phytoplankton and zooplankton were enumerated and correlated with the abundance of schistosomiasis snails in the sites. The results indicated significantly more Biomphalaria sudanica snails than Bulinus africanus snails in different physical habitats on land (Student's t‐test, P < 0.05), as well as in different locations on land (Student's t‐test, P = 0.026). Regression analyses revealed that several physicochemical parameters, including dissolved oxygen (R² = −0.659; n = 8; P = 0.014), pH (R² = 0.728; n = 8; P = 0.007) and turbulence (R² = −0.616; n = 8; P = 0.02), were predictive of Biomphalaria spp. abundance, while pH (R² = 0.610; n = 8; P = 0.02) and turbulence (R² = −0.578; n = 8; P = 0.028) were predictive of Bulinus spp. abundance in different locations in the lake. Cyanobacteria (R² = 0.638; n = 8; P = 0.02) and chlorophyceae (R² = −0.50; n = 8; P = 0.05) were shown to be predictive of both Biomphalaria spp. and Bulinus spp. abundance in different locations in the lake. Zooplankton abundance varied significantly between different locations in the lake (One‐way anova, P < 0.001). Bosmina spp. were found to be predictive of both Biomphalaria spp. (R² = −0.627; n = 8; P = 0.01) and Bulinus spp. (R² = −0.50; n = 8; P = 0.05) in different locations in the lake. The results from this study will help inform policy regarding control measures for schistosomias and intermediate snail hosts in Lake Victoria waters, as well as in adjacent terrestrial aquatic habitats and even beyond.

The objective of this study was to evaluate the risks associated with nutrient and heavy metal pollution in the water and sediments of Kouris Reservoir in Cyprus, and to recommend applicable measures to alleviate them. The reservoir drainage area contains various historic abandoned copper mines existing in an ophiolite geological substrate. Kouris Reservoir water is classified as oligotrophic to mesotrophic, with phosphorus being the limiting factor for algae growth. The thermal stratification of the reservoir enhances anoxic conditions in the reservoir hypolimnion, initiating phosphorus release back into the water column from the lake bottom sediments. The increased phosphorus release, in combination with increased water temperatures during the summer months (i.e. reaching 27 °C in August), may be the key factors enhancing the growth of microbial communities and cyanobacteria blooms. The sediment of Kouris Reservoir is classified as ‘low risk’ on the basis of the Ecological Risk Index scheme, in contrast to the Geoaccumulation Index, which indicates a moderate degree of contamination for chromium (Cr), nickel (Ni) and copper (Cu), and a high degree for lead (Pb). Heavy metals are strongly bound to the sediment matrix at pH values between 7 and 9, but can be released back into the water column at potential acid pH values. In addition, the sediments exhibit a high copper and chromium absorption affinity under current water quality conditions in the reservoir, as shown by batch absorption experiments. The experimental results suggest dredging of the reservoir sediment, and its subsequent dumping of the sediments near influent streams, would have adverse effects on the environment in the event of acid rain or other environmental changes that might acidify the sediment.