The relative effects of enrichment and climate change on the long‐term dynamics of Daphnia in Esthwaite Water, Cumbria

Abstract

1. The factors influencing the seasonal and inter-annual variations in the numbers of Daphnia hyalina in Esthwaite Water between 1956 and 1972 are analysed. Esthwaite Water has always been eutrophic, but the phosphorus and nitrogen loadings to the lake increased significantly in the mid 1960s.2. Qualitatively, the phytoplankton and zooplankton populations in the lake changed relatively little during the period of study. Quantitatively, however, eutrophic species of algae became more abundant and the numbers of Eudiaptomits declined as the numbers of Daphnia increased.3. The seasonal dynamics of the Daphnia was governed partly by the seasonal temperature cycle, and partly by the periodicity of edible algae. The birth rate of the Daphnia was constrained by temperature from January to April and from October to December. At other times their rate of increase was governed by the relative abundance of edible and inedible algae.4. Edible and inedible species of algae tended to appear in a recurring annual sequence. Diatoms such as Asterionella were abundant in the spring, the early summer phytoplankton was dominated by edible flagellates, but inedible algae such as Aphanizomenon and Microcystis become dominant later in the year.5. Daphnia could only reproduce in late summer when there were periodic regrowths of edible algae. Such regrowths were most likely to occur when there had been some entrainment of deep nutrients by episodic wind mixing. Calm weather encouraged the growth of blue-green algae that effectively 'blocked' the development of the Daphnia for the remainder of the summer.6. The factors that controlled the seasonal dynamics of the Daphnia also influenced the average number recorded in a particular year. The average number of Daphnia increased in the early sixties when Cryptomonas was abundant and decreased in ihe late sixties when blooms of Aphanizomenon appeared in mid summer. Detailed analyses showed that a similar increase in the numbers of Aphanizometion had occurred in the late fifties. The critical factor throughout was the prolonged period of calm resulting in stable stratification. 7, This 'weather' effect was highlighted by comparing de-trended timeseries of Daphnia and Aphanizometion numbers with a simple measure of thermocline stability. De-trending removed the superimposed effects of progressive enrichment and revealed a 10-year cycle of thermocline stability that matched the temperature cycle recently reported in Windermere, These cycles are related to the movement of weather systems in the Atlantic so could change if the pattern of atmospheric circulation is altered by global warming.8. The possible effects of climate change on Daphnia dynamics are discussed in relation to the findings in Esthwaite Water.

Evaluation of Spatial-Temporal Variations of Water Quality and Plankton Assemblages and Its Relationship to Water Use in Kulekhani Multipurpose Reservoir, Nepal

“…The observed zooplanktons' diversity in the present study couples with the average surface water temperature of the reservoir, with a significant correlation coefficient (R = 0.62). Similar, associations between temperature and zooplanktons have been previously reported in several water bodies [42] [43] [44]. In addition to the reservoir temperature, transparency, pH and alkalinity also showed positive correlation with the planktons' diversity and abundance in the reservoir water.…”

Climate change and freshwater zooplankton: what does it boil down to?

“…Increased stratification and reduced mixing also can cut nutrient flux from deeper layers. As a consequence, nutrient conditions in the epilimnion can be limiting for algae (George et al 1990) and decreased phytoplankton production can lead to the starvation of zooplankton; for instance, in Esthwaite Water, strongly reduced Daphnia abundance in ''calm years'' was assumed to be the result of food limitation because shallow mixing hampered algal growth through nutrient depletion (George 2000). Daphnids, however, may benefit directly from stratification through a positive response to increased water temperatures and/or indirectly via increased phytoplankton productivity (Straile and Geller 1998).…”

Contribution of sediment focussing to heterogeneity of organic carbon and phosphorus burial in small lakes

“…The biological, chemical and physical characteristics of the lake have been previously described (Mortimer, 1941;Sutcliffe et al, 1982;Talling & Heaney, 1988;George et al, 1990;George, 2000). High-resolution meteorological data were …”