Linda May - Academia.edu (original) (raw)

Papers by Linda May

Lakes & Reservoirs: Science, Policy and Management for Sustainable Use, 2021

We present a GIS‐based approach to the delineation of areas that have different levels of suitabi... more We present a GIS‐based approach to the delineation of areas that have different levels of suitability for use as tilapia cage culture sites the Kenyan part of Lake Victoria, Africa. The study area was 4,100 km2. The method uses high‐resolution bathymetric data, newly collected water quality data from all major fishing grounds and cage culture sites, and existing spatial information from previous studies. The parameters considered are water depth, water temperature, levels of dissolved oxygen, chlorophyll‐aconcentrations, distances to the lake shoreline and proximity to other constraints on cage culture development. The results indicated that the area most suitable for fish cages comprised about 362 km2, or approximately 9% of the total area; the remaining 91% (i.e., 3,737 km2) was found to be unsuitable for tilapia cage culture. We conclude that the successful implementation of this approach would need stakeholder involvement in the validation and approval of potential sites, and in...

Environmental Pollution, 2019

Water, 2019

Agricultural activities are responsible for most of the nitrogen (N) inputs that degrade water qu... more Agricultural activities are responsible for most of the nitrogen (N) inputs that degrade water quality. To elucidate the drivers leading to N pressures on water, we examined the resulting state of surface waters in terms of N concentrations, the impact of this on water quality status and policy responses to these constraints across different climatic and management conditions. Portugal and Denmark were chosen as contrasting case studies for the Driver-Pressure-State-Impact-Response (DPSIR) analysis. Our results showed reductions of 39% and 25% in the use of mineral fertilizer in Portugal and Denmark, respectively, between 2000 and 2010. The N surplus in Portugal varied between 15 and 30 kg N ha−1 between 1995 and 2015. In Denmark, in 2015, this amount was 70 kg N ha−1, representing a 53% decrease from the 1990 value. The average amount of total N discharged to surface waters was 7 kg ha−1 for mainland Portugal in 2015 and 14.6 kg ha−1 for Denmark in 2014. These reductions in the N s...

Science of The Total Environment, 2018

The Science of the total environment, Jan 20, 2016

Nutrient emissions in human waste and wastewater effluent fluxes from domestic sources are quanti... more Nutrient emissions in human waste and wastewater effluent fluxes from domestic sources are quantified for the UK over the period 1800-2010 based on population data from UK Census returns. The most important drivers of change have been the introduction of the water closet (flush toilet) along with population growth, urbanization, connection to sewer, improvements in wastewater treatment and use of phosphorus in detergents. In 1800, the population of the UK was about 12 million and estimated emissions in human waste were 37kt N, 6.2kt P and 205ktorganicC/year. This would have been recycled to land with little or no sewage going directly to rivers or coastal waters. By 1900, population had increased to 35.6 million and some 145kt N were emitted in human waste but, with only the major urban areas connected to sewers, only about 19kt N were discharged in sewage effluent. With the use of phosphorus in detergents, estimated phosphorus emissions peaked at around 63.5ktP/year in the 1980s, w...

Marine and Freshwater Research, 2013

Water quality monitoring programs are often based upon low-frequency regular sampling regimes fro... more Water quality monitoring programs are often based upon low-frequency regular sampling regimes from which loads are estimated. In this study, stream flow (Q) and phosphorus concentrations (C) were measured at 2-hourly intervals over a 10-week period between October and December 2006 in a tributary of Loch Leven, Scotland. The dataset was deconstructed to emulate different weekly, daily and composite sampling strategies, the aim being to highlight the large amount of uncertainty and imprecision in estimating total (TP) and soluble reactive (SRP) phosphorus loads on the basis of commonly applied sampling strategies and calculation methods. When based on the full dataset, phosphorus (P) loads estimated from the 2-hourly data were 459 kg TP, 351 kg particulate P (PP) and 78 kg SRP. In contrast, P loads estimated from different weekly, daily and composite sampling regimes and determined by applying seven different calculation methods ranged from 22 to 5028 kg TP, 13 to 4588 kg PP and 7 to...

IOP Conference Series: Earth and Environmental Science, 2020

Eutrophication affects many lakes and reservoirs worldwide. It is caused by excessive amounts of ... more Eutrophication affects many lakes and reservoirs worldwide. It is caused by excessive amounts of nutrients entering waterbodies from their catchments, mainly due to human activity. The main sources of these nutrients are discharges from industry and wastewater treatment systems, and agricultural runoff. The water quality problems caused by eutrophication, such as harmful algal blooms, affect the sustainable use of lakes for agriculture, fisheries, recreation, tourism and water supply. They also degrade habitat quality and threaten biodiversity. A range of methods for improving lake water quality are explored, including catchment management and in-lake restoration measures. The potential impacts of these on lake biodiversity are explored, including species interactions and ecosystem feedbacks that may confound the recovery process. A particular challenge is the fact that achieving sustainable recovery may take many years, mainly due to the impact of legacy pollution problems. This mu...

International Journal of Environmental Research and Public Health, 2020

Phosphorus is one of the main causes of waterbodies in Scotland being at less than good ecologica... more Phosphorus is one of the main causes of waterbodies in Scotland being at less than good ecological status (GES) in terms of the water framework directive (WFD). In Scotland, there are more than 8000 standing waters, defined as lakes and reservoirs that have a surface area of more than 1 hectare. Only about 330 of these are monitored routinely to assess compliance with the WFD. The export coefficient tool PLUS+ (phosphorus land use and slope) has been developed to estimate total phosphorus (TP) concentrations in the unmonitored sites; modelled values are then compared to WFD target concentrations for high, good, moderate, poor, and bad status to assess compliance. These type-specific or site-specific targets are set by the regulatory authority and form part of a suite of physical, chemical, and ecological targets that are used to assess GES, all of which must be met. During development, the PLUS+ tool was applied to 323 monitored catchments and 7471 unmonitored catchments. The effica...

Hydrobiologia, 2019

There may be differences between this version and the publisher's version. You are advised to con... more There may be differences between this version and the publisher's version. You are advised to consult the publisher's version if you wish to cite from this article. Article (refereed)-postprint May, Linda; Wallace, Robert L. 2019. An examination of long-term ecological studies of rotifers: comparability of methods and results, insights into drivers of change and future research challenges.

Estonian Journal of Ecology, 2014

This review summarizes winter conditions from six polymictic European shallow lakes. The lakes ra... more This review summarizes winter conditions from six polymictic European shallow lakes. The lakes range from oligotrophic to hyper-eutrophic. Four of the lakes freeze regularly while ice cover is absent or rare in the two others. Ice duration and timing of ice-out are significantly influenced by climate signals in three of the lakes. Winter water temperature remains higher in nonice-covered lakes. No long-term trend in temperature is detectable except for one lake where winter water temperature began to increase in 1986. Secchi depth in winter is equal or greater than summer values in all six lakes indicating relatively better light conditions in winter. Total phosphorus concentration in winter ranges from 10 to 130 µg L-1 , which is equal or lower than summer values and is unrelated to chlorophyll a in five of the sites. Phytoplankton species composition during winter differs largely at the six sites. The winter assemblages largely depend on the trophic level and the conditions during the previous season. Winter chlorophyll a and phytoplankton biomass are usually lower than summer values because of reduced photosynthetic rates. Bacterial production often exceeds primary production. Epipelic algal assemblages tend to proliferate during winter in both ice-covered and non-ice-covered lakes. Primary production is low during winter because of insufficient light. Zooplankton abundances and biomass critically depend on conditions during the previous season and the winter situation and are quite variable from year to year, but their values correlate with the trophic status of the lakes. As a result, winter conditions are important to understand seasonal and annual changes in shallow lakes.

Water Science and Technology, 2006

This paper reviews the progress made towards the restoration of Loch Leven, the largest lake in l... more This paper reviews the progress made towards the restoration of Loch Leven, the largest lake in lowland Scotland, over the last 20 years. In particular, the importance of direct regulation and of setting water quality objectives and targets is examined. Various means of engaging with stakeholders and the general public are also considered. Success criteria and catchment management initiatives are described and briefly reviewed.