Debate surrounds the best way to deal with pond terrestrialization so as to maximize landscape-scale biodiversity. One way of addressing this issue is to re-set succession via management activities, but the merits of this approach relative to non-intervention and pond creation are little known. Manor Farm in Norfolk, UK, possesses around 40 ponds, and each year three to four ponds are subject to management involving tree (de-shading) and/or sediment removal. To determine the consequences of management for pond biodiversity, macrophyte and invertebrate communities were surveyed for replicate ponds covering four ???time since management??? categories: no management, and managed over the periods 1999???2003, 2004???2006 and 2007???2009. Macrophyte diversity was significantly lower in unmanaged ponds compared with ponds managed in 2004???2006 and 2007???2009. In addition, with the exception of Mollusca, invertebrate diversity was significantly lower in the unmanaged ponds compared with all the managed ponds. A tendency was evident for diversity to peak 3???5 years after management and for a subsequent decline in diversity (significant for macrophytes). No distinctive species assemblages were associated with the different pond successional stages, although several species were confined to individual ponds. Although many species were absent from the non-managed ponds, especially in the macrophytes and Coleoptera, few species were unique to these ponds. The principal driver of species turnover in the ponds was shade, which was negatively correlated with macrophyte cover. Shade was substantially higher in the unmanaged ponds, whose species-poor assemblages appeared to be a consequence of low oxygen levels. By arresting succession and restoring macrophyte-dominated early- and mid-successional ponds, management may have an essential role in biodiversity conservation. In pond-rich landscapes, where a high proportion of ponds are heavily terrestrialized, management provides a sustainable means both of preserving heterogeneity in the pond network and preventing the loss of large numbers of species which favour early- and mid-successional pond

Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer diel ranges in their near-surface temperatures of between 4 and 7°C. Large diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored.

No abstract

Summary1. Anthropogenic nitrogen (N) deposition may have several impacts on upland moorland ecosystems, including changes in vegetation composition, eutrophication and surface water acidification through nitrate leaching, but few studies linking N deposition to key biogeochemical processes have been published. A stable isotope tracer (15 N) was used to determine the fate of inorganic N inputs to four moorland catchments across gradients of N deposition and leaching, through 2-weekly additions to experimental plots on major soil types over 1 year.3. An apparent decline in total 15 N recovery from soils and vegetation as the proportion of leached N deposition increased was not significant at the P = 0·05 level, but a significant relationship was found for recovery in mosses and lichens. 4. Vegetation retained 31-68% of 15 N inputs, and 15 N recovery increased significantly ( P = 0·01) with biomass for all compartments except woody shrubs. Mosses and lichens showed far greater 15 N recovery per unit biomass than grasses or ericaceous shrubs. There was no significant variation in the proportion of 15 N recovered in higher plants across the N deposition gradient (24-29%). In contrast, the proportion recovered in mosses and lichens declined from 44% to 2% as deposition increased, mirroring a decline in their biomass and showing a highly significant inverse relationship ( P = 0·01) with nitrate leaching. The proportion of15 N recovered in litter plus surface soils (33-39%) was remarkably constant across the deposition gradient for a variety of soil types. However, significantly declining recovery per unit biomass in litter ( P < 0·05) suggested progressive N saturation of this sink and increasing importance of retention in underlying surface soils as deposition increased. 6. Synthesis and applications . Past studies have demonstrated a decline in mosses and lichens in response to increasing N deposition, but we show here for the first time that reduced N retention might result together with increased nitrate leaching into surface waters. The conservation of bryophyte and lichen flora on moorlands is therefore critical to prevent excessive nitrate leaching and associated surface water acidification and eutrophication. Ensuring management practices such as grazing or burning are at an intensity that does not further degrade the bryophyte and lichen communities may help minimize the impact of N deposition on freshwaters, but the only effective means to reduce the risk of N leaching is a reduction in N emissions.