Optimising water quality monitoring to understand biogeochemical processes in UK rivers and reservoirs

Elfferich, Inge 2024. Optimising water quality monitoring to understand biogeochemical processes in UK rivers and reservoirs. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis explores how high-frequency sensor data can improve understanding of environmental and biogeochemical conditions in inland water bodies, particularly for predicting cyanobacteria-related taste and odour (T&O) compounds geosmin and 2-MIB in drinking water reservoirs. Since these compounds cannot be directly measured in situ, alternative predictors are required. High-frequency hydrochemical sensor data from six UK rivers showed that a minimum measurement frequency of four hours was required to capture the necessary variation in the parameters. For T&O prediction, key drivers need to be identified that high-frequency sensors can measure. These drivers were studied in laboratory microcosms with reservoir water, which found that nutrient ratios (N:P and NH4+:NO3-) and concentrations impacted phytoplankton productivity, community composition and the production of 2-MIB. 2-MIB production was linked to benthic cyanobacteria (Leptolyngbya spp. and Pseudanabaena spp.) and community productivity, with total nitrogen being a stronger predictor than nutrient ratios, but P-limitation also played a role. NH4+ caused rapid ‘boom-bust’ growth, while NO3- led to more balanced growth four days later. Long-term manual sampling and sensor data from 2022-2023 in the same reservoir showed that optimal weather conditions led to increased productivity and a delayed T&O response. Geosmin concentrations (likely from planktic cyanobacteria) increased 1-2 weeks after high solar energy and low rainfall, while 2-MIB (likely from benthic cyanobacteria) was linked to high temperatures and low wind gusts 2-3 weeks earlier. While N:P and NH4+:NO3- ratios were direct predictors of geosmin and 2-MIB, these are not useful for an early-warning system, because elevated NH4+ and PO43- concentrations were likely related to internal loading and T&O release after cell death. The most useful predictors were environmental parameters that support phytoplankton growth (seasonality, solar energy, air temperature, precipitation and wind speed), indirect growth indicators (dissolved oxygen, vertical mixing), and measurements of inflows to the reservoir via a tributary (NO3--N, PO43--P, NH4+-N or EC and turbidity, alongside discharge). Appropriate in situ measurement of these factors, especially when combined with weather forecasts, can provide early warnings of T&O events that can guide water treatment management.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Earth and Environmental Sciences
Funders:	NERC
Date of First Compliant Deposit:	28 March 2025
Last Modified:	28 Mar 2025 14:25
URI:	https://orca.cardiff.ac.uk/id/eprint/177251

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