The role of vegetation in the water budget of the Usangu wetlands, Tanzania

The Usangu wetlands were severely degraded over the last twenty years by cattle and the shortage of water due to rice irrigation upstream. The eastern Usangu wetlands that were previously perennial dried out in 2000 and 2002 in the dry season. Following the removal of cattle in 2006 from the eastern Usangu wetlands, perennial wetlands has re-established itself and in 2011 the vegetation had recovered and covered about 95?% of the wetted surface mainly as floating vegetation. These wetlands are the source of water of the Great Ruaha River and the volume of water entering the river has nearly doubled after cattle removal. We suggest that this may be due to the shading effect of the floating vegetation reducing the loss of water through net evaporation to about 0.5?cm?day^?1 as opposed to about 1?cm?day^?1 for open water evaporation in this tropical climate. This suggests the important role of the biology in controlling the water budget. By contrast cattle and rice farms have not been removed from the western Usangu wetlands, located upstream, where the wetlands are now reduced to small areas fringing the rivers. We suggest that the western Usangu wetlands should also be restored in order to further increase flows in the Great Ruaha River. At the same time water governance in the catchments and irrigation areas upstream of Usangu wetlands is also urgently required because present water yields are insufficient to meet the hydroelectric needs of Tanzania, the water users all along the river, as well as the important coastal wetlands associated with the Rufiji Delta during a drought year.     

Wildlife water utilization and importance of artificial waterholes during dry season at Ruaha National Park, Tanzania

Provision of water to wildlife is crucial during dry season along the Great Ruaha River (GRR) in Ruaha National Park due to mismanagement of water resources upstream. This paper shows that wildlife in the dry areas of the park utilizes effectively the water from natural and artificial waterholes dug in the sandy riverbed of the GRR. Artificial water holes help alleviate the effects of artificial water shortage in the river, and because the location of the artificial water holes varies annually, the impact on the vegetation of aggregating herbivores around water holes was minimized. Water quality was comparable in natural and artificial water holes, and was the highest in holes dug by elephants in the sandy river bed.     

Colonisation by Dreissena of Great Lakes coastal ecosystems: how suitable are wetlands?

1.  Invasive zebra ( Dreissena polymorpha ) and quagga mussels ( Dreissena bugensis ) have become widespread throughout the Great Lakes basin. However, some types of Great Lakes coastal wetlands may be unsuitable for Dreissena invasion.
2.  To test this observation, artificial substrata were placed in wetlands (with emergent vegetation) and in adjacent open water (without emergent vegetation) habitats in two types of Great Lakes coastal ecosystems: drowned river mouth (DRM) and coastal fringing systems. Wetlands in DRM systems generally have deep organic sediment and limited water movement, whereas coastal fringing wetlands generally have low to moderate amounts of organic sediment and intense wind and wave action.
3.  We did not find a significant difference in Dreissena colonisation between wetlands and adjacent open water habitat in fringing systems. However, Dreissena colonisation was significantly lower in DRM wetlands than in the adjacent open water. We also found significantly lower survival in DRM wetlands than adjacent open water habitats, whereas survival did not differ significantly in coastal fringing wetlands and the adjacent open water.
4.  Our results suggest that vulnerability to Dreissena invasion varied among wetland types with DRM wetlands being less suitable than fringing wetlands. We suggest that colonisation and survival of Dreissena is lower in wetlands with deep organic sediment and less turbulent water.     

Towards an ecohydrology-based restoration of the Usangu wetlands and the Great Ruaha River, Tanzania

An open channel flow model, calibrated against field data, suggests that cattle intrusion in the eastern Usangu wetlands, as well as both dry and wet weather irrigation upstream, are responsible for the seasonal drying out of the Great Ruaha River (GRR) downstream. This human-induced change has severe socio-economic implications downstream, including hindering hydroelectricity production, as well as a devastating impact on the Ruaha National Park (RNP) ecosystem that is now shifting from wet tropics to dry tropics. To ensure sustainable development, governance is urgently needed for the Usangu catchment in a way that is compatible with ecohydrology principles for the sustainable use of water resources. In order to do that, perennial flow must be restored to the GRR. For this to happen this study suggests that all the livestock must be removed from the eastern Usangu wetlands and dry weather irrigators must return at least 25% (∼4 m³ s⁻¹) of the water to the river.     

Water circulation and fish larvae recruitment in papyrus wetlands,Rubondo Island,Lake Victoria

A field study was undertaken of the hydrodynamics, water quality and adult and larval fish abundance in papyrus wetlands and surrounding coastal waters at Rubondo Island, Lake Victoria. Because they were exposed to the prevailing wind, the two bays facing east had small (0.01 km²) wetlands and were well flushed, with minimal accumulation of organic detritus and little oxygen depletion. Because it faced west, the third bay, Mlaga Bay, was sheltered and poorly flushed; organic matter accumulated in a large (1.41 km²) papyrus wetland. The rises and falls of the lake level at decadal time scales, may, by drowning or drying out wetlands, contribute significantly to storing organic matter as detritus. Vegetation decay in the wetlands, as well as primary production, resulted in large diurnal fluctuations of pH and dissolved oxygen concentration. Shading in daytime and cooling at night, cooled the wetlands water sufficiently to generate a baroclinic circulation whereby cold, wetland water sank and moved offshore in the lake while warm, lake water intruded in the wetlands near the surface. This flushing prevented the occurrence of anoxic conditions in the wetlands which were used by adult and larval fish, mainly tilapia, and freshwater shrimps (Caridina nilotica). No fish larvae were found at more than 150 m from the shore in the three bays. Both larval fish and Caridina nilotica appeared to move in and out of the wetlands at night, possibly as a result of low dissolved oxygen as well as sheltering from predation. Their abundance varied with the lunar phase, with maximum near new moon and first quarter. Being the only protected wetlands in Lake Victoria, Rubondo Island may increasingly become an important source of replenishment for fisheries in the lake which elsewhere appears overfished.     

Papyrus wetlands a lunar-modulated refuge for aquatic fauna

A field study was undertaken of the use of papyrus (Cyperus papyrus) wetlands fringing Rubondo Island, Lake Victoria, Tanzania, as a refuge from predators by freshwater shrimps (Caridina nilotica) and tilapia (Oreochromis niloticus) larvae. During the full moon nights, fish larvae took refuge more than 5 m in the papyrus and did not venture out into the lake, while they ventured into fringing lake waters during moonless nights. The freshwater shrimps and lake flies (Chaoborus sp.) did not migrate with the moon. This fauna took refuge in the papyrus wetlands even though the dissolved oxygen concentration was as low as 0.4 ppm (<5% of saturation).     

Associations between water quality, Pasteurella multocida, and avian cholera at Sacramento National Wildlife Refuge

We studied patterns in avian cholera mortality, the presence of Pasteurella multocida in the water or sediment, and water chemistry characteristics in 10 wetlands at the Sacramento National Wildlife Refuge Complex (California, USA), an area of recurrent avian cholera epizootics, during the winters of 1997 and 1998. Avian cholera outbreaks (>or=50 dead birds) occurred on two wetlands during the winter of 1997, but no P. multocida were recovered from 390 water and 390 sediment samples from any of the 10 wetlands. No mortality events were observed on study wetlands during the winter of 1998; however, P. multocida was recovered from water and sediment samples in six of the 10 study wetlands. The pH levels were higher for wetlands experiencing outbreaks during the winter of 1997 than for nonoutbreak wetlands, and aluminum concentrations were higher in wetlands from which P. multocida were recovered during the winter of 1998. Water chemistry parameters (calcium, magnesium, sodium, and dissolved protein) previously linked with P. multocida and avian cholera mortality were not associated with the occurrence of avian cholera outbreaks or the presence of P. multocida in our study wetlands. Overall, we found no evidence to support the hypothesis that wetland characteristics facilitate the presence of P. multocida and, thereby, allow some wetlands to serve as long-term sources (reservoirs) for P. multocida.     

FISH AND FISHERIES OF WETLANDS

SUMMARY

The three major wetland types have characteristic fish communities. River-associated wetlands harbour a rich diversity of fishes which can either survive habitat desiccation during the dry-down, or migrate to and fro with the flood. Endorheic wetlands have a lower diversity of species which are typically ‘r’-selected relative to mainstream riverine or lacustrine forms. Marine wetlands have a variety of peripheral or marine forms, but are not discussed in this account. The dynamics of wetland fish communities are determined by periodically changing abiotic factors, especially water temperature and water level, and biotic factors, especially food availability. Water level fluctuations have several important functions and result in pulses of nutrient input and fish abundance. Wetland fish stocks can usually be sustained as long as the pristine flood regime is retained, but disruption of the flooding pattern interferes with fish breeding and nutrient flow. Fishing yields may be directly correlated with the flood history during the previous two years. Wetland fishes play an important role by converting the resource at the base of the food chain, i.e. living plants, detritus or epiphytes, into food for higher trophic levels. The need to identify and conserve key food supplies is emphasized. Wetland fisheries are relatively poorly developed in southern Africa with notable exceptions, e.g. Pongolo floodplain, Okavango swamp, Lake Liambezi, Elephant Marsh on the Shire River, but even in these systems the resource is probably underutilized.

The need to consider the socio-economic implications of upgrading a subsistence fishery are emphasized, and further study on the effect of water level fluctuations on major trophic pathways and on multispecies fisheries is encouraged. Because of the urgent need to manage wetland fisheries, various short-cut methods to obtain first-order estimates of fish production, yields and growth rates should be used until more data are available. The need to manage a floodplain holistically for both the aquatic and terrestrial phases is stressed. In addition, inocula (re-colonizing life history stages) should be conserved to accelerate the recovery of endorheic wetland fish stocks after a drought. As wetlands are of fundamental importance to lake or river metabolism and provide vital breeding and feeding areas for fishes, they should be given the highest conservation priority. Cost-benefit analyses should therefore be performed before any large scale manipulations of wetlands are performed.     

Chemical and physical factors associated with yellow perch abundance in Great Lakes coastal wetlands: patterns within and among wetland types

Great Lakes coastal wetlands provide important spawning and nursery habitat as well as abundant food resources for yellow perch (Perca flavescens). We examined multiple years of fyke-net data from wetlands along Lakes Huron and Michigan to describe yellow perch distribution in drowned river mouth (DRM) and coastal fringing systems. Principal components analysis and multi-response permutation procedures indicated that DRM wetlands (yellow perch CPUE = 0.2) were eutrophic systems that often exhibit high temperatures and periods of hypoxia, whereas coastal fringing wetlands (yellow perch CPUE = 32.1) were less productive. Among the coastal fringing systems, Saginaw Bay (Lake Huron), displayed characteristics of being more productive and had more yellow perch. Most yellow perch captured in Saginaw Bay were age-0, suggesting that it was an important nursery habitat. Among DRM ecosystems, we found that the downstream lake macrohabitats contained more yellow perch than upstream wetlands; however, there was no significant difference in abiotic characteristics to explain the higher catches in lakes. We hypothesize that yellow perch were more prevalent in wetlands with intermediate productivity during summer because these systems provide abundant food resources without the harsh conditions associated with highly eutrophic wetlands.     

Annual and non-annual fish assemblages respond differently to environmental and spatiotemporal variations of temporary wetlands from southern Brazil

• The fish community of temporary wetlands is highly dynamic due to the marked seasonal changes in hydrological and limnological conditions. In this study, we evaluated spatiotemporal variation in the fish community and the influence of environmental factors on this variation in temporary wetlands in southern Brazil.
• Two different life cycles—annual and non-annual fishes—were recorded among species. Variation in the fish community appeared to be associated with differences in the life history strategy of species. While species of annual fish were present throughout the hydroperiod, gradually decreasing in density over time, non-annual fish species had an opposite pattern, with higher densities in the final phase of the hydrological cycle.
• Variations in the composition and abundance of fish community in temporary wetlands were related to habitat and landscape attributes (area, number of microhabitats and isolation between temporary wetlands) and climate indicators of water availability (air temperature, average rainfall, and water level of the São Gonçalo channel), but not to water conditions (dissolved oxygen, pH, conductivity and water temperature).
• We concluded that the ichthyofauna of temporary wetlands are composed both of rare species, highly specialised for life within these ephemeral environments, and widespread generalist species that reach the wetlands opportunistically for short periods. Habitat and landscape attributes and changes in climate and hydrological variables over the hydroperiod are the factors that had the greatest influence on spatiotemporal variation of the fish community.
• Maintaining physical characteristics and the hydrological cycle of temporary wetlands is critical for the conservation of fish species inhabiting these vulnerable environments in southern Brazil. Habitat and landscape attributes and climate and hydrology fluctuations affect the annual and non-annual fishes inhabiting temporary wetlands differently.

     

Hurricane storm surge and amphibian communities in coastal wetlands of northwestern Florida

Isolated wetlands in the Southeastern United States are dynamic habitats subject to fluctuating environmental conditions. Wetlands located near marine environments are subject to alterations in water chemistry due to storm surge during hurricanes. The objective of our study was to evaluate the effect of storm surge overwash on wetland amphibian communities. Thirty-two wetlands in northwestern Florida were sampled over a 45-month period to assess amphibian species richness and water chemistry. During this study, seven wetlands were overwashed by storm surge from Hurricane Dennis which made landfall 10 July 2005 in the Florida panhandle. This event allowed us to evaluate the effect of storm surge overwash on water chemistry and amphibian communities of the wetlands. Specific conductance across all wetlands was low pre-storm (<100 μS/cm), but increased post-storm at the overwashed wetlands ([`(x)] \bar{x}  = 7,613 μS/cm). Increased specific conductance was strongly correlated with increases in chloride concentrations. Amphibian species richness showed no correlation with specific conductance. One month post-storm we observed slightly fewer species in overwashed compared with non-overwashed wetlands, but this trend did not continue in 2006. More species were detected across all wetlands pre-storm, but there was no difference between overwashed and non-overwashed wetlands when considering all amphibian species or adult anurans and larval anurans separately. Amphibian species richness did not appear to be correlated with pH or presence of fish although the amphibian community composition differed between wetlands with and without fish. Our results suggest that amphibian communities in wetlands in the southeastern United States adjacent to marine habitats are resistant to the effects of storm surge overwash.     

Rehabilitation of Swamp Paperbark (<Emphasis Type="Italic">Melaleuca ericifolia</Emphasis>) wetlands in south-eastern Australia: effects of hydrology,microtopography, plant age and planting technique on the success of community-based revegetation trials

Wetlands dominated by Swamp Paperbarks (Melaleuca spp., Myrtaceae) are common in coastal regions across Australia. Many of these wetlands have been filled in for coastal development or otherwise degraded as a consequence of altered water regimes and increased salinity. Substantial resources, often involving community groups, are now being allocated to revegetating the remaining wetland sites, yet only rarely is the effectiveness of the rehabilitation strategies or on-ground procedures robustly assessed. As part of a larger project investigating the condition and rehabilitation of brackish-water wetlands of the Gippsland Lakes, we overlaid a scientifically informed experimental design on a set of community-based planting trials to test the effects of water depth, microtopography, plant age and planting method on the survival and growth of seedlings of Melaleuca ericifolia Sm. in Dowd Morass, a degraded, Ramsar-listed wetland in south-eastern Australia. Although previous laboratory and greenhouse studies have shown M. ericifolia seedlings to be salt tolerant, the strongly interactive effects of waterlogging and salinity resulted in high seedling mortality (>90%) in the field-based revegetation trials. Seedlings survived best if planted on naturally raised hummocks vegetated with Paspalum distichum L. (Gramineae), but their height was reduced compared with seedlings planted in shallowly flooded environments. Age of plants and depth of water were important factors in the survival and growth of M. ericifolia seedlings, whereas planting method seemed to have little effect on survival. Improved testing of revegetation methods and reporting of success or otherwise of revegetation trials will improve the effectiveness and accountability of projects aiming to rehabilitate degraded coastal wetlands.     

Submerged macrophytes, zooplankton and the predominance of low- over high-chlorophyll states in western boreal, shallow-water wetlands

1. Shallow‐water (<2 m deep) wetlands in northern Alberta's western boreal forest tend to have either extremely high‐chlorophyll, pea‐green water or water that is low in chlorophyll and clear. The relative importance of top‐down processes (e.g. zooplankton grazing) compared with bottom‐up processes (e.g. nutrient limitation) for regulating the existence of these alternate states has yet to be explicitly investigated in these poorly studied waterbodies. 2. To assess the relationship between chemical and biological factors and the predominance of low‐chlorophyll over high‐chlorophyll states, a survey of 24 shallow‐water wetlands in northern Alberta was conducted over the summers of 2001 and 2002. 3. In wetlands without fish, statistical analysis indicated that high‐ and low‐chlorophyll sites could be differentiated with 82% accuracy based solely on whether submerged aquatic vegetation (SAV) coverage was greater or less than 25%. Further, high‐SAV lakes with zooplankton communities dominated by large cladocerans were clear 96% of the time. 4. In the few wetlands that supported stickleback populations, large cladocerans were absent. However, the development of zooplankton communities dominated by small cladocera (Bosmina) with calanoid copepods in fish‐containing wetlands corresponded with a shift from high‐ to low‐chlorophyll states. 5. Results suggest that in fishless wetlands high‐SAV coverage and grazing by large, SAV‐associated cladocerans promotes low‐chlorophyll states. Results also suggest that suppression of macroinvertebrate predators by sticklebacks allowing Bosmina to flourish may also promote low‐chlorophyll, clear‐water conditions.     

Species-area relationship and environmental predictors of fish communities in coastal freshwater wetlands of southern Brazil

In the Neotropics where fragmentation is common, environmental factors structuring fish communities are poorly known. In this study two hypotheses were tested in 13 coastal wetlands of southern Brazil: 1) physical features (such as wetland area, habitat diversity, water depth and temperature, and water and sediment chemistry) are important determinants of richness, density and composition of fish assemblages; and 2) species richness and composition of fish assemblages differ between wetlands with different hydroperiods (i.e. permanent versus intermittent). A total of 1,597 individuals distributed among 20 species were collected. Richness was positively associated with wetland area and water depth and it was negatively associated with water conductivity. The species-area power function explained 27.3% of the variation in richness. Fish richness was similar between permanent and intermittent wetlands. The density was negatively associated with water depth and temperature, and it was positively correlated with water nitrate concentration. The first three axes from the CCA accounted for 55.5% of total variation in fish composition. The most important variables related to fish composition were percentage of sediment organic matter, phosphorus concentration, habitat diversity and water depth. Composition of fish species changed among permanent and intermittent wetlands. Understanding the environmental factors that shape and maintain the biodiversity in these ecosystems is essential to develop conservation and management programs of wetlands in this region, where more than 90% of wetland systems have already been lost due to anthropogenic activities.     

The influence of wetlands, decaying organic matter, and stirring by wildlife on the dissolved oxygen concentration in eutrophicated water holes in the Seronera River, Serengeti National Park, Tanzania

The dissolved oxygen concentration (DO) was sampled during a diurnal cycle in three water holes heavily used by wildlife and with distinctive biological features along the Seronera River. The DO fluctuated widely (by up to 11.5 mg l⁻¹) as a function of time, mechanical stirring and aeration by animals, and the presence of fringing wetlands. The DO cycle was successfully modeled (within 0.3 mg l⁻¹) by assuming that the four dominant processes were photosynthesis and respiration by algae near the surface, trapping by wetlands, decomposition of dead organic matter on the bottom, and stirring/aeration by hippos. The rate of DO decline from the decay of dead organic matter was equal to the rate of DO removal by algal respiration at night.     

Species‐specific responses to wetland mitigation among amphibians in the Greater Yellowstone Ecosystem

Habitat loss and degradation are leading causes of biodiversity declines, therefore assessing the capacity of created mitigation wetlands to replace habitat for wildlife has become a management priority. We used single season occupancy models to compare the occurrence of larvae of four species of pond‐breeding amphibians in wetlands created for mitigation, wetlands impacted by road construction, and unimpacted reference wetlands along a highway corridor in the Greater Yellowstone Ecosystem, United States. Created wetlands were shallow and had less aquatic vegetation and surface area than impacted and reference wetlands. Occupancy of barred tiger salamander (Ambystoma mavortium) and boreal chorus frog (Pseudacris maculata) larvae was similar across wetland types, whereas boreal toads (Anaxyrus boreas) occurred more often in created wetlands than reference and impacted wetlands. However, the majority of created wetlands (>80%) dried partially or completely before amphibian metamorphosis occurred in both years of our study, resulting in heavy mortality of larvae and, we suspect, little to no recruitment. Columbia spotted frogs (Rana luteiventris), which require emergent vegetation that is not common in newly created wetlands, occurred commonly in impacted and reference wetlands but were found in only one created wetland. Our results show that shallow created wetlands with little aquatic vegetation may be attractive breeding areas for some amphibians, but may result in high mortality and little recruitment if they fail to hold water for the entire larval period.     

Macroinvertebrate community structure across a wetland hydroperiod gradient in southern New Hampshire,USA

We conducted a field study to examine the influence of hydroperiod and concomitant changes in abiotic (wetland size, pH, conductivity, dissolved oxygen and water temperature) and biotic (predatory fish presence) characteristics on macroinvertebrate communities in isolated wetlands in southern New Hampshire. Invertebrates were sampled using dipnet sweeps in 42 wetlands with short (<4 months), intermediate (4–11 months) or long (permanent) hydroperiods in 1998 and 1999. We found that invertebrate genera richness, and to a lesser degree abundance, increased linearly along the hydrological gradient, and in response to temperature and dissolved oxygen. Relative abundance of genera also differed markedly with respect to hydroperiod. Most notably, invertebrate communities changed from Acilius-dominated communities to Notonecta-dominated communities. Invertebrate relative abundances in permanent wetlands also differed with respect to the occurrence of predatory fish. Some genera (e.g., Libellula, and Dytiscus) were more likely to occur in permanent wetlands without fish, whereas other genera (e.g., Buena, and Basiaeshna) were more likely to occur in wetlands with predatory fish. Because aquatic invertebrate communities differed markedly with respect to wetland hydroperiod, and in relation to the occurrence of predatory fish, it is essential to retain a diversity of wetlands in the landscape to ensure the long-term persistence of aquatic invertebrate biodiversity.     

Changes in aquatic vegetation and fish communities following 5 years of sustained low water levels in coastal marshes of eastern Georgian Bay,Lake Huron

Aquatic vegetation in the relatively pristine coastal wetlands of eastern Georgian Bay provides critical habitat for a diverse fish community. Declining water levels in Lake Huron over the past decade, however, have altered the wetland plant assemblages in favour of terrestrial (emergent and meadow) taxa and have thus reduced or eliminated this important ecosystem service. In this study, we compared IKONOS satellite images for two regions of eastern Georgian Bay (acquired in 2002 and 2008) to determine significant changes in cover of four distinct wetland vegetation groups [meadow (M), emergent (E), high‐density floating (HD) and low‐density floating (LD)] over the 6 years. While LD decreased significantly (mean ?2995.4 m²), M and HD increased significantly (mean +2020.9 m² and +2312.6 m², respectively) between 2002 and 2008. Small patches of LD had been replaced by larger patches of HD. These results show that sustained low water levels have led to an increasingly homogeneous habitat and an overall net loss of fish habitat. A comparison of the fish communities sampled between 2003 and 2005 with those sampled in 2009 revealed that there was a significant decline in species richness. The remaining fish communities were also more homogeneous. We suggest that the observed changes in the wetland plant community due to prolonged low water levels may have resulted in significant changes in the fish communities of coastal wetlands in eastern Georgian Bay.     

Millennial-scale change in the structure of a Caribbean reef ecosystem and the role of human and natural disturbance

Caribbean coral reefs have transformed into algal-dominated habitats over the past half-century, but the role of specific anthropogenic drivers is unresolved due to the lack of ecosystem-level data predating human disturbance. To better understand the extent and causes of long-term Caribbean reef declines, we produced a continuous 3000-yr record of the ecosystem state of three reefs in Bocas del Toro, Caribbean Panama. From fossils and sediments obtained from reef matrix cores, we tracked changes in reef accretion rates and the taxonomic and functional group composition of fish, coral, urchin, bivalve and benthic foraminifera. This dataset provided a comprehensive picture of reef community and environmental change. At all sites, reefs shifted from systems with greater relative abundance of herbivorous fish, epifaunal suspension feeding bivalves and Diadema urchins to systems with greater relative abundance of micropredator fish, infaunal bivalves and Echinometra urchins. These transitions were initiated a millennium ago at two less-degraded reefs fringing offshore islands and ~250 yr ago at a degraded patch reef near the continental coast. Ecosystem shifts were accompanied by a decline in reef accretion rates, and at the patch reef, a decline in water quality since the 18th century. Within all cores, synchronous increases in infaunal bivalves and declines in herbivorous fish regardless of water quality suggest a loss of hard substrate and increasingly hypoxic sediment conditions related to herbivore loss. While the early timing of ecosystem transitions at the fringing reefs implicates large-scale hydrological change, the more recent timing of change and loss of water quality at the patch reef implicates terrigenous runoff from land-clearing. Our whole-ecosystem reconstruction reveals that reef ecosystem deterioration appears to follow a predictable trajectory whether driven by natural or anthropogenic disturbances and that historical local human activities have quickly unraveled reefs at a scale similar to longer-term natural environmental change.     

Enhancing the fish production potential of Lake Victoria papyrus wetlands,Kenya, using seasonal flood-dependent ponds

We present the findings of a participatory experiment on integrated aquaculture-agriculture systems (Fingerponds) at the Lake Victoria wetlands, Kenya. Fingerponds are flood-based lacustrine or floodplain wetland fishponds. The aim of the study was to explore, within a wetland/floodplain interface environment, the potential of semi-intensive fish production to enhance the wetland fishery and protect the natural ecosystem from wide-scale, destructive encroachment. The ponds were stocked naturally by flood water. After flood recession, livestock manure was added to the ponds and the effects of manuring on water and sediment quality and fish yields were studied. Manuring had positive effects on the nitrogen, phosphorous and chlorophyll a concentrations of the pond water. Regression analysis results indicated that site, manuring and environmental and climatic variables explained 58–70% of the variation in dissolved nitrogen and phosphorous, and 71% of the variation in chorophyll a. Manuring enhanced the total phosphorus concentration in the sediment but it only had marginal effects on total nitrogen. Although the net fish yields were highly variable between sites and seasons, ranging from 402 to 1069 kg ha⁻¹, the data showed that manuring was advantageous. The duration of the culture period, site variability and manuring explained 82% of the variation in fish yields. We conclude that Fingerponds fertilized with livestock manure from abutting riparian subsistence agriculture can improve fish production, enhance food diversity and security and contribute to more efficient use of papyrus wetlands for food production. This in turn may reduce large-scale conversion of wetlands to agriculture.