1. Technical summary: Environmental Systems Project
Project title: A Trophic Study of the University of York’s Heslington East Lake
Author: Thomas Alan Sheppard
Please note that this summary is restricted to 1 page only,do not exceed this limit
Researchquestion/issue addressed by project:
The report aimed to determine whether the concentration of inorganic nutrients and chlorophyll α (a
proxy for phytoplankton biomass) around the reed beds on the perimeter of the lake represented a
body of water that could sustain a healthy ecosystem. The trophic state of the lake was determined
and in turn so was the effectiveness of the Sustainable Urban Drainage Systems, notably the reed
beds, incorporated into the campus landscape to filter nutrients from surface runoff. The intention
was to assist the University’s Site Management Team and provide recommendations on the reduction
of nutrient inputs from the wider landscape.
Summary of the methods and approaches used: Triplicate surface water samples were collected on
the 10th November 2016 at equal distances either side of each reed bed, totalling five beds and ten
sites upon the 10.4 hectare lake situated on the southern margin of the site. After filtering, samples
were analysed using an autosampler and fluorometer to measure the concentrations of phosphate,
nitrate, ammonium, and the concentration of chlorophyll α respectively. The autosampler relies upon
a colourimetric technique to determine concentrations of nutrients after undergoing a reaction to
produce a coloured dye. The flourometer measures the fluorescence of extracted chlorophyll a
pigment.
Key findings: Nitrate and ammonium concentrations differed significantly across the three sections
of the lake, in line with chlorophyll α. Concentrations were highest in section one, decreasing through
sections two and three. A strong positive correlation existed between concentrations of nitrate and
ammonium with chlorophyll. This relationship was further supported by chlorophyll α concentrations
in section three, reflecting low concentrations of nitrate and ammonium. At the majority of sites,
inorganic nitrogen and nitrate concentrations were thought unlikely to stimulate algal growth to a
significant degree, as they were within the range appropriate for a mesotrophic ecosystem (0.3 -
0.65𝑚𝑔𝑁𝑙−1
and <0.2 𝑚𝑔𝑁𝑂3 𝑙−1
respectively). The contrary was observed in section one,
particularly at sites A2 and B2 where the chlorophyll concentration was at its highest. Phosphate
concentrations did not differ significantly across the lake sections, and the relationship with
chlorophyll α was weak and insignificant. Phosphorus concentrations were however, considerably
higher than those of natural surface waters (>0.020 𝑚𝑔𝑃𝑂4 𝑙−1
). Based upon chlorophyll and
phosphate concentrations, the lake is marginally to severely eutrophic at the majority of sites.
Inorganic nitrogen was considered to have the greatest influence on phytoplankton biomass. Rainfall
was light and unlikely to have disturbed lake sediment in the shallow margins the week preceding the
collection of samples.
Recommendations: The effectiveness of current management systems, notably the Sustainable
Urban Drainage Systems requires review. The eutrophic state of the lake suggests a reduction in
inorganic nitrogen and phosphorus loading is required throughout. Particular attention needs to be
directed upon sections one and two. Improving the condition of the reed beds may be just one way of
reducing nutrient inputs. Water residence times within individual lake sections should also be
investigated, as nutrients may otherwise accumulate. Moreover, the condition of the retention basin
feeding into section one also requires investigation as it may elevate nutrient concentrations.