Long-term trends in Loch Leven invertebrate communities

Abstract

Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. This paper has not been submitted elsewhere in identical or similar form, nor will it be during the first three months after its submission to Hydrobiologia. 2 AbstractDetailed studies of the macroinvertebrate benthos and zooplankton communities in Loch Leven, the largest shallow lowland lake in Scotland, UK, were carried out from 1966 to 1973 as part of the International Biological Programme (IBP). The results revealed a reduction in species diversity that was attributed to increasing eutrophication. This work provides a baseline against which the response of the invertebrate communities to subsequent changes in management can be assessed. This paper compares macroinvertebrate benthos and zooplankton data from the IBP study with the post-IBP era during which changes at Loch Leven included a 60% reduction in the phosphorus input from external sources and variations in fish stocking rates. Only in recent years has there been evidence of ecological recovery by the invertebrate communities: the number of macroinvertebrate and zooplankton taxa has increased (including taxa considered to be sensitive to nutrient enrichment) and invertebrate abundances have declined. These changes appear to reflect the improvements in water quality and habitat conditions at Loch Leven that have occurred as a result of the recent reduction in nutrient loads, albeit with a substantial delay before any ecological response could be detected. This time lag in recovery has important implications for assessing improvements in the ecological status of other lake systems, as is required by the EU Water Framework Directive.3

Identifying from recent sediment records the effects of nutrients and climate on diatom dynamics in Loch Leven

“…As a result of the catchment management plan, P concentrations in Loch Leven declined from an annual mean in excess of 100 μg TP L −1 in the early 1970s to 33 μg TP L −1 in 2008, which meets the water quality target of 40 μg TP L −1 annual mean for restoring the ecological health of the loch set by the Loch Leven Area Management Advisory Group (LLAMAG, 1993). The declining trend was nonlinear, however, with a rapid decline in concentrations in the early 1970s thought to be largely because of the return of Daphnia to the lake in 1970 after an absence of 15–20 years (Gunn et al. , in press), a slight increase in the early 1990s caused by P recycling from the sediments (Carvalho et al.…”

“…Nevertheless, Fozzard et al. (1999), May & Carvalho (2010) and Gunn et al. (in press) report signs of positive ecological change in the loch since the reduction in point sources of P, including lower algal abundances, increased water clarity, increased macrophyte colonisation depth, and an increased diversity and abundance of invertebrates.…”

“…The rapid decline in TP concentrations in the early 1970s (Fig. 6) pre‐dates the restoration programme and is again thought to be largely because of the return of Daphnia in 1970 following their disappearance, attributed to dieldrin poisoning (Morgan, 1970; Gunn et al. , in press).…”

Habitat Complexity in Aquatic Microcosms Affects Processes Driven by Detritivores

“…These three species often co-occur (e.g. [18]) and while all species compete for the leaf resources added [13–15], we expected the copepod Cyclops (much smaller than Asellus and Gammarus ) to profit from the presence of other species. Copepods can feed on faeces [19] and they mainly feed on the microbes decomposing leaves rather than the leaves themselves (as Asellus and Gammarus do).…”

Ecological relevance of anabranch confluences: Hydrological and morphological effects

“…We speculated that s-s5 was sampled during the so-called colonization in progress (Blettler et al, 2016). This phenomenon could be attributed to a short time lag or brief delayed response of organisms to environmental changes (Gunn, O'Hare, Maitland, & May, 2012;Sukhodolov, Blettler, Zhang, Sukhodolova, & Nützmann, 2015); that is, a short period is required to guarantee invertebrate colonization after the sandy-patches settling.…”