Diatom dissolution in saline lake sediments: an experimental study in the Great Plains of North America

Environmental reconstructions are limited by the quality of the original data from which they are derived. In situations where microfossils are poorly preserved problems may arise, both through taxonomic uncertainty and more subtly from the alteration of the death assemblage as a result of the differential robustness of species. Diatom dissolution tends to be a particular problem in saline lakes. Laboratory-based dissolution experiments on fresh, modern diatoms collected from lakes in North and South Dakota and Saskatchewan were carried out to establish the abundance and composition changes of assemblages as dissolution progressed. Analysis of experimental results demonstrates that species exhibit regular dissolution relationships and can be ranked according to susceptibility to dissolution. Changes in valve morphology for selected key taxa were categorised under scanning electron and light microscopy into 'dissolution stages'. These data provide the basis for developing dissolution indices for individual taxa and assemblages, which can be related to absolute abundance changes of diatom valves. Experimental data were applied to two separate weighted averaging (WA) transfer functions to predict measured dissolution parameters (such as dissolved silica) and to a salinity transfer function developed from the Northern Great Plains. In the former case, models incorporating dissolution stage counting were more accurate and robust (as validated by jackknifing). Species and samples were downweighted according to species robustness (dissolution rank) within the WA transfer function. Downweighting either, or both, species and samples in the transfer function algorithm lead to minor improvements in model performance in terms of both r2 and standard error (as RMSE), despite incomplete coverage of species. A short core from Spiritwood Lake, North Dakota, was used to test the differences variable weighting had on reconstructed salinity. Results suggest Spiritwood Lake is only responsive to more extreme climatic events, and has remained fresh (<0.5g/l TDS) or subsaline (0.5-<3g/l TDS) throughout the last 150 years. The approach of variable sample and species weighting to the rest of the NGP surface sediment assemblage training set may improve the model further, which could be tested at sites with an historical record of salinity

Anthropogenic alteration of nutrient supply increases the global freshwater carbon sink

Lakes have a disproportionate effect on the global carbon (C) cycle relative to their area, mediating C transfer from land to atmosphere, and burying organic-C in their sediments. The magnitude and temporal variability of C burial is, however, poorly constrained, and the degree to which humans have influenced lake C cycling through landscape alteration has not been systematically assessed. Here, we report global and biome specific trajectories of lake C sequestration based on 516 lakes and show that some lake C burial rates (i.e., those in tropical forest and grassland biomes) have quadrupled over the last 100 years. Global lake C-sequestration (~0.12 Pg year-1) has increased by ~72 Tg year-1 since 1900, offsetting 20% of annual CO2 freshwater emissions rising to ~30% if reservoirs are included and contributing to the residual continental C sink. Nutrient availability explains ~70% of the observed increase, while rising temperatures have a minimal effect

Macroinvertebrate Diversity in Urban and Rural Ponds: Implications for Freshwater Biodiversity Conservation

Ponds are among the most biodiverse freshwater ecosystems, yet face significant threats from removal, habitat degradation and a lack of legislative protection globally. Information regarding the habitat quality and biodiversity of ponds across a range of land uses is vital for the long term conservation and management of ecological resources. In this study we examine the biodiversity and conservation value of macroinvertebrates from 91 lowland ponds across 3 land use types (35 floodplain meadow, 15 arable and 41 urban ponds). A total of 224 macroinvertebrate taxa were recorded across all ponds, with urban ponds and floodplain ponds supporting a greater richness than arable ponds at the landscape scale. However, at the alpha scale, urban ponds supported lower faunal diversity (mean: 22 taxa) than floodplain (mean: 32 taxa) or arable ponds (mean: 30 taxa). Floodplain ponds were found to support taxonomically distinct communities compared to arable and urban ponds. A total of 13 macroinvertebrate taxa with a national conservation designation were recorded across the study area and 12 ponds (11 floodplain and 1 arable pond) supported assemblages of high or very high conservation value. Pond conservation currently relies on the designation of individual ponds based on very high biodiversity or the presence of taxa with specific conservation designations. However, this site specific approach fails to acknowledge the contribution of ponds to freshwater biodiversity at the landscape scale. Ponds are highly appropriate sites outside of protected areas (urban/arable), with which the general public are already familiar, for local and landscape scale conservation of freshwater habitats

Nutrients and Saltwater Exchange as Drivers of Environmental Change in a Danish Brackish Coastal Lake over the Past 100 Years

Many northwest European lake systems are suffering from the effects of eutrophication due to continued loading and/or poor, ineffective management strategies. Coastal brackish lakes are particularly difficult to manage due to complex nitrogen, phosphorus, and salinity dynamics that may exert varying influence on lake biological communities, but long-term data on how these important and often biodiverse systems respond to change are rare. In this study, palaeolimnological data (including sedimentary parameters, diatoms, and plant macrofossils) and environmental monitoring data (for the last ~40 years) have been used to assess environmental change over the last 100 years in Kilen, a brackish lake in northwest Jutland, Denmark. Kilen has been regularly monitored for salinity (since 1972), TP (from 1975), TN (from 1976), and since 1989 for biological data (phytoplankton, zooplankton, and macrophytes), which allows a robust comparison of contemporary and paleolimnological data at high temporal resolution. The palaeolimnological data indicate that the lake has been nutrient rich for the last 100 years, with eutrophication peaking from the mid-1980s to the late 1990s. Reduced nutrient concentrations have occurred since the late 1990s, though this is not reflected in the sediment core diatom assemblage, highlighting that caution must be taken when using quantitative data from biological transfer functions in paleolimnology. Lake recovery over the last 20 years has been driven by a reduction in TN and TP loading from the catchment and shows improvements in the lake water clarity and, recently, in macrophyte cover. Reduced salinity after 2004 has also changed the composition of the dominant macrophyte community within the lake. The low N:P ratio indicates that in summer, the lake is predominately N-limited, likely explaining why previous management, mainly focusing on TP reduction measures, had a modest effect on the water quality of the lake. Despite a slight recovery, the lake is still nutrient-rich, and future management of this system must continue to reduce the nutrient loads of both TN and TP to ensure sustained recovery. This study provides an exceptional opportunity to validate the palaeolimnological record with monitoring data and demonstrates the power of using this combined approach in understanding environmental change in these key aquatic ecosystems

Reply to “Marine abundance and its prehistoric past in the Baltic”

In response to the comment by Hausmann et al.1 we highlight here that a number of the key criticisms of Lewis et al.2 are either misinterpretations of our paper or are speculative, requiring rigorous testing via empirical data (and subsequently are topics for further research). We would, therefore, like to take the opportunity to clarify these points, so that others do not misinterpret our study2 in the same way. Hausmann et al.1 provide no physical evidence or data that rebuke our hypothesis, and therefore in the spirit of critical scientific discussion and endeavour, we challenge them (or others) to disprove our hypothesis through high-quality data, and hope that our original paper2 and this further discussion stimulate such work. The criticisms expressed by Hausmann et al. largely focus on the use of a summed probability distribution 14C curve based on oysters as a proxy for shell midden abundance, yet this is only a supportive dataset within the broader theme of this study, and we certainly welcome future research into improving how we quantify shell midden abundance and marine resource intensification in past cultures and societies. However, we highlight that the criticisms of this 14C oyster-derived dataset by Hausmann et al.1 does not detract from the key point of this study, that population increased during periods of increased marine productivity (demonstrated by sediment pigment and other proxy data) and hence increased marine resource availability, when humans predominately consumed a marine-based diet3. Below we respond to the specific points raised by Hausmann et al.1. </p

A late glacial and holocene record of biological and environmental changes from the crater Lake Albano, Central Italy: an interdisciplinary European project (Paliclas)

This paper reports the results of biological analyses (pigments, diatoms, chrysophyte cysts, cladocerans, chironomids and ostracods) of a ca. 14 m-long sediment core recovered from Lake Albano (Central Italy) in the course of the EU-funded project PALICLAS (PALaeoenvironmental analysis of Italian Crater Lake and Adriatic Sediments). A reconstruction of the environmental evolution and ecosystem response of Lake Albano during the last ca. 30 kyr was possible. Additional information on lake level oscillation is obtained from benthic and planktonic palaeocommunities. Several oscillations in the productivity and the level of the lake were detected in the oldest sediment layers (from ca. 30 kyr BP to ca. 17 kyr BP), followed by a long (ca. 5 kyr BP) period of low productivity in which cold, holomictic conditions prevailed. A period of high biological activity and, probably, meromictic conditions during the early-mid Holocene was detected. A clear impact of human activities in the catchment was found at ca. 4 kyr BP in the form of increased erosion, associated with a decline in the abundance of biological remains. Further signs of human impact on the lake ecosystem are recorded during the Roman period. Although large-scale environmental changes (e.g. regional climate changes) caused many of the observed biological changes, human activities were important during the mid-late Holocene

Shedding off-the-grid: The role of garment manufacturing and textile care in global microfibre pollution

Textile fibres are abundant anthropogenic pollutants. These fibres enter aquatic, terrestrial, and atmospheric environments, and biota. Textile fibres pose biological and chemical threats to the environments they pollute. Laundry is a primary source of synthetic and natural textile fibres. Fibre shed from laundry performed in electric washing machines is well characterised. However, over 50% of the global population does not have regular access to an electric washing machine. Without regular access to an electric washing machine, people launder ‘Off-the-grid’ with locally specific methods. Their variable laundry methods present a significant challenge to quantifying microfibre shed. This study makes an original contribution to studies of fibre shedding. First, it details laundry protocols in a Global South community. Second, it assesses how textile structure influences fibre shedding independent of laundry practices. To do this, we deploy a hand-laundry protocol learned during ethnographic fieldwork. We show that hand-washed garments shed fibres in numbers comparable to machine-washed garments. We show how garment construction (knit and weave) influences fibre shedding. We find fibre type (cotton or polyester) does not. People who hand wash clothing cannot change practices contributing to textile fibre pollution. Thus, industry must act to minimise fibreshed from laundry at the global scale. This entails transforming the design, manufacture, and sale of textiles