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We examine the degradation of the natural capital and ecosystem services of an important tropical lake, Kenya's Lake Naivasha, in the context of human activities and exploitation since the mid-20th century. These factors have culminated in the recent emergence of innovative governance arrangements with potential contributions to the future sustainability of the lake ecosystem.
Lake Naivasha maintains high ecological interest and biodiversity value despite its food web being controlled, at three trophic levels, by alien species for the past 40 years. The lake now has very high economic value, being the centre of Kenya's floricultural industry, itself the top foreign exchange earner for the country. It became internationally-renowned in 1999 as one of the first wetland sites worldwide to be nominated by the government for Ramsar status as a result of local action, guided by the Lake Naivasha Riparian Association (LNRA). This led, in 2004, to gazettement by the Kenyan Government for the management of the lake by a Committee under LNRA guidance.
By 2010, however, progress towards sustainable management was limited, not least because the lake water had continued to be over-exploited for irrigation, geothermal power exploration and domestic supplies outside the catchment. A prolonged drought in Kenya in 2009–10, in conjunction with this ongoing over-exploitation, caused the lake level to recede to the lowest since the late 1940s and brought the ecological degradation to global attention. Arguably, this new prominence catalysed the political interventions which now offer new hope of progress towards a sustainable lake basin.
We examine the ecological changes over the past 40 years and the reasons why new management regimes instituted over the past 10 years have to date been unable to halt ecological degradation of the lake and its environs. We outline a future trajectory that links new governance initiatives with a wider network of stakeholders which, together with external interventions that have been initiated in 2011, may well help to restore the ecosystem's health.
Stratospheric ozone concentrations are not expected to recover to pre-ozone hole levels until the mid-21st century and, even after ozone recovery, climate and other anthropogenic changes will continue to alter ultraviolet radiation (UV) exposure regimes in aquatic ecosystems. Although our understanding of the ecology of UV continues to move towards a new paradigm that emphasises complex interactive and indirect effects of UV on communities of organisms, rather than simple direct negative effects on individuals, considerable uncertainty remains regarding the impacts of sustained or changing UV stress on aquatic ecosystems. In this synthesis we examine the importance of indirect UV effects for some key ecosystem level characteristics and processes in lakes. We draw particular attention to the implications of UV for disease dynamics, contaminant toxicity, biodiversity, and carbon cycling in lakes. Although UV has strong lethal mutagenic and chronic physiological effects on organisms, we suggest that indirect effect pathways, including UV effects on animal behaviour, food quality, and trophic interactions are likely to be important in lake ecosystem dynamics.
The phytobenthos of streams has received a renewed interest since the introduction of the European Water Framework Directive (WFD), with all European member states now being required to monitor stream phytobenthos. This review highlights the reasons for using the phytobenthos as a monitoring tool in water bodies and examines the various biomonitoring approaches adopted. The different possible indices and metrics used for determining the ecological status of a stream using the phytobenthos are evaluated in terms of how effective and inclusive they are. The biological, chemical and physical niches that the phytobenthos occupies in streams are also considered, as well as the functional importance of the phytobenthos to the stream ecosystem as the primary energy source. Multiple factors, such as hydrology, nutrients and grazers, influence phytobenthic growth in streams and these are discussed. All these factors have the potential to limit or enhance phytobenthic growth in different situations and are often interlinked, meaning that the influence of each is difficult to tease apart. This review, however, attempts to look at the current knowledge regarding each factor and discuss how it influences phytobenthic growth in the context of other factors, if such multiple interactions have been researched.