Community monitoring of coliform pollution in Lake Tanganyika

Conventional water quality monitoring has been done for decades in Lake Tanganyika, under different national and international programs. However, these projects utilized monitoring approaches, which were temporally limited, labour intensive and costly. This study examines the use of citizen science to monitor the dynamics of coliform concentrations in Lake Tanganyika as a complementary method to statutory and project-focused measurements. Persons in five coastal communities (Kibirizi, Ilagala, Karago, Ujiji and Gombe) were trained and monitored total coliforms, faecal coliforms and turbidity for one year on a monthly basis, in parallel with professional scientists. A standardized and calibrated Secchi tube was used at the same time to determine turbidity. Results indicate that total and faecal coliform concentrations determined by citizen scientists correlated well to those determined by professional scientists. Furthermore, citizen scientist-based turbidity values were shown to provide a potential indicator for high FC and TC concentrations. As a simple tiered approach to identify increased coliform loads, trained local citizen scientists could use low-cost turbidity measurements with follow up sampling and analysis for coliforms, to inform their communities and regulatory bodies of high risk conditions, as well as to validate local mitigation actions. By comparing the spatial and temporal dynamics of coliform concentrations to local conditions of infrastructure, population, precipitation and hydrology in the 15 sites (3 sites per community) over 12 months, potential drivers of coliform pollution in these communities were identified, largely related to precipitation dynamics and the land use

D2.1 Report on analysis of the requirements for MONOCLE sensors including projection of cost-savings and stakeholder feedback. Deliverable report of project H2020 MONOCLE (grant 776480)

Requirements for MONOCLE sensors were analysed at the start of sensor development, particularly with regard to projected cost-savings in monitoring and specific stakeholder feedback. The main inputs from stakeholders were obtained from the MONOCLE water quality monitoring survey (D9.1) and are used here to define sensor-specific development priorities, particularly with respect to purpose, performance, cost and interoperability. This document guides both the initial development of new sensors and evolution of existing prototypes to higher technological readiness levels

Citizen scientists filling knowledge gaps of phosphate pollution dynamics in rural areas

In situ monitoring is fundamental to manage eutrophication in rivers and streams. However, in recent decades, the frequency and spatial coverage of regulatory monitoring have often been reduced due to funding and infrastructure limitations. This reduction has made it impossible to provide adequate coverage for most water bodies. In this study, trained citizen scientists filled spatial and temporal gaps in agency monitoring across a major catchment in rural England. By integrating data from citizen scientists, regulatory agencies, and the local water company, it was possible to demonstrate the opportunities for hypothesis-based citizen scientist monitoring to identify continuous and event-driven sources of phosphate pollution. Local citizen scientists effectively covered important spatial gaps, investigating river conditions both upstream and downstream of suspected pollution point sources, improving the identification of their temporal dynamics. When combined with long-term monitoring data from regulatory agencies, it became possible to identify areas within the catchment that exhibited increased phosphate concentrations during periods of low river discharge (summer). Inter-annual trends and anomaly detection suggested that continuous pollution sources dominated over event-driven sources in many sub-basins, allowing for the prioritisation of mitigation actions. This study highlights the opportunity for citizen scientists to fill gaps in regulatory monitoring efforts and contribute to the improved management of eutrophication in rural catchments

Land use related silica dynamics in terrestrial ecosystems.

Silicon (Si) provides the base component for well-balanced food-webs in aquatic systems. Here, together with nitrogen and phosphorous Si determines phytoplankton composition, and plays a major role in eutrophication problems and carbon sequestration. Rivers are the primary source of Si for the oceans, and is ultimately derived from mineral weathering. However there is growing evidence illustrating the importance of biological Si cycling in terrestrial ecosystems. Riverine Si fluxes will be affected by biological and pedological processes. Human perturbations, like land-use change will alter Si dynamics in these ecosystems, and in turn final Si delivery to rivers. Although acknowledged, the effects of human perturbations on the size and composition of the Si flux from land to ocean are poorly quantified. In order to fully understand the effect of human perturbations, two scientific challenges are addressed in this thesis. First, the thesis focuses on developing a clear quantitative understanding of bio-available Si (TSi = amorphous (ASi) + dissolved (DSi)) mobilisation processes in cultivated and natural landscapes. Second, this thesis attempts to couple historical land use changes with Si dynamics, specifically mobilisation and storage processes of Si. As a first step, we confirmed that the alkaline digestion method proposed by DeMaster can be used for runoff samples provided the solid to solution ratio is within certain limits., We derived recommendations for ASi analysis based on our findings, making a distinction between samples with low and high suspended particulate matter. However, one should be aware that the range and limits for solid to solution ratio proposed here may depend on the type of sediment to be analysed. Rainfall experiments were conducted to simulate initial Si mobilisation through soil erosion at small plot scale. A simple field survey of in situ measurements of experimental conditions (i.e. static parameters) was insufficient to model final ASi delivery. A mixed model based on only the dynamic parameters, i.e. sediment and runoff properties, made it possible to accurately estimate ASi mobilisation for different crop and tillage techniques. Interrill erosion mobilises a disproportionate amount of ASi. In terms of ASi fluxes, lower enrichment at higher suspended particulate matter is counteracted by increasing soil loss rates, and are therefore determined by the erosive power. At catchment scales, other water erosion processes become important as well as size-selective scale effects including infiltration and (re-)deposition. Therefore it is suggested that a combination of increased water erosion processes and harvesting of crops (i.e. biomass and soil loss) will result in a depletion of the soil ASi pool over time, and influence Si delivery to aquatic systems. A comparison of catchments with specific dominant land uses showed mainly within-channel mobilisation determines final ASi mobilisation in forested and pasture sites. For DSi, a conceptual model was proposed that explains the observed dilution-flushing effect during runoff events. An end-member mixing analysis proved that groundwater delivery seems to control Si delivery from the forest and pasture site. Although our measurements of DSi concentrations suggested a non-chemostatic behaviour for Si, we showed Si loads from forests and pastures strongly depend on specific runoff, and therefore did act as a chemostatic system. A relatively stable signal confirms there is an important kinetic equilibrium mobilised Si becomes rapidly replaced to generate a constantly high signature - at catchment scale. In the arable catchment the contribution of ASi and therefore surface runoff was more important, and will drastically alter the relative abundance of ASi versus DSi in rivers. Here, the fate of the mobilised ASi is largely unknown; within river rapid dissolution of ASi may counterbalance lower base-flow delivery of DSi. This highlights that detailed studies at small scales remain invaluable to evaluate the validity of general principles. In terms of agricultural expansion, we confirmed the finding that Si dynamics are altered in a rapidly cultivated landscape. At the pasture site, deforestation led to decreased Si concentrations but did not alter Si delivery as specific discharge had risen. In contrast, land use conversion to arable land not only altered Si solubility in soil but also lowered final Si delivery in highly cultivated catchments. Enhanced ASi mobilisation by soil erosion was insufficient to replenish the lowered DSi fluxes. Our Belgian results were corroborated by findings from total bio-available Si soil pools along a Swedish land use gradient. Here, differences in size and distribution are interpreted as the long-term effect of reduced ASi replenishment, as well as changes in ecosystem specific pedogenic processes and increased mobilisation of the bio-available Si in disturbed soils. Past agricultural expansion in temperate regions has led to an important reduction in TSi delivery. To fully understand the effect of land use change, an integral Si budget (pools and riverine fluxes) is necessary. This study assessed for the first time the initial Si delivery from different ecosystems. On larger scales, they need to be integrated with the sequestration of ASi in reservoirs and rivers, the increasing contribution of ground water flow and the biological uptake within aquatic systems. A changing climate will drastically alter not only the vegetation-soil processes, but also the hydrology of a region. The acquired knowledge with respect to how the Si dynamics in catchments react to changing land use is valuable to predict the effects of climate change and develop sustainable nutrient management strategies for aquatic systems.Voorwoord I Summary V Samenvatting IX Table of Contents XIII List of figures XVII List of tables XXI List of symbols and abbreviations XXIII Chapter 1 Problem statement and research questions 1 1.1 Background 1 1.2 Research Questions 6 1.3 Thesis Outline 9 PART I: Silica mobilisation in relation to land uses Chapter 2 Amorphous silica analysis in terrestrial runoff samples 13 2.1 Introduction 13 2.2 Materials & Methods 15 2.2.1 Sample preparation 15 2.2.2 Laboratory analysis 16 2.2.3 Statistical analysis 17 2.3 Results 18 2.4 Discussion 20 2.4.1 Solution domains 20 2.4.2 Error Compensation 22 2.4.3 Effect of σ on ASi measurements 24 2.4.4 Method adaption 26 2.5 Conclusion & Recommendations 29 Chapter 3 Mobilisation of Amorphous Silica on Small Agricultural Plots 31 3.1 Introduction 31 3.2 Materials and Methods 32 3.2.1 Study Area 32 3.2.2 Rainfall Experiments 35 3.2.3 Statistical analysis 37 3.3 Results 40 3.3.1 ASi dissolution 40 3.3.2 Overview 41 3.3.3 Field conditions 44 3.3.4 Sediment and runoff properties 46 3.3.5 Fluxes of ASi 49 3.4 Discussion 49 3.5 Conclusions 54 Chapter 4 Seasonal dynamics of Si fluxes in a forested catchment 57 4.1 Introduction 57 4.2 Materials & Methods 60 4.2.1 Study area 60 4.2.2 Field Methods 60 4.2.3 Laboratory Methods 62 4.2.4 Load & Flux Calculations 63 4.3 Results 64 4.3.1 Discharge 64 4.3.2 Si concentrations 66 4.3.3 Suspended Particulate Matter 67 4.3.4 Silica loads and fluxes 69 4.4 Discussion 74 4.4.1 Temporal dynamics of Si fluctuations 74 4.4.2 Si dynamics in a forested catchment: a conceptual model 76 4.4.3 DSi as a tracer for geochemical hydrograph separation 79 4.4.4 Detailed Si fluxes from a forested catchment 89 4.5 Conclusions 92 Chapter 5 Land use control on dissolved and amorphous silica transport and pathways 95 5.1 Introduction 95 5.2 Materials & Methods 97 5.2.1 Study area 97 5.2.2 Field Methods 99 5.2.3 Laboratory Methods 101 5.2.4 Flux Calculations 101 5.3 Results 102 5.3.1 Silica concentration 102 5.3.2 Silica fluxes 107 5.4 Discussion 110 5.4.1 Effect of land use on Si solubility 110 5.4.2 Processes responsible for Si delivery 111 5.4.3 Effect of land use on Si delivery from low-order catchments 114 5.5 Conclusions 118 PART II Silica storage and human impact Chapter 6 Anthropogenic impact on amorphous silica pools in temperate soils 123 6.1 Introduction 123 6.2 Materials and Methods 125 6.2.1 Study Area 125 6.2.2 Field Sampling 126 6.2.3 Laboratory Analysis 128 6.3 Results 129 6.3.1 Distribution of amorphous silica 129 6.3.2 Distribution of easily soluble silica 132 6.3.3 Physical and chemical soil properties 135 6.4 Discussion 135 6.4.1 Human impacts 135 6.4.2 Amorphous silica and organic carbon 137 6.4.3 Historical deforestation: An estimate for temperate regions of the effect on ASi pools. 138 6.5 Conclusion 144 Chapter 7 General conclusions and recommendations for future research 147 7.1 General conclusions 147 7.2 Recommendations for further research 155 References 161nrpages: 178status: publishe

Amorphous Silica Transport in the Ganges Basin : Implications for Si Delivery to the Oceans

Rivers transport ∽6 x1012 mol yr-1 of dissolved Si (DSi) from the continents to the oceans. They also carry amorphous silica (ASi), solid phases likely to dissolve in seawater. Unfortunately, the magnitude of this flux is poorly constrained at a global scale. We present 92 new ASi values from suspended particulate matter (SPM) from the Ganges basin. Bulk SPM is ∽1.2% ASi, and mean ASi concentrations are ∽65 μM, of comparable magnitude to DSi concentrations. Our results also indicate a) ASi is not evenly distributed in the water column of large rivers, b) the ASi is not a wholly biogenic Si endmember and c) the ASi flux is, to a first order, a function of the SPM load. Our results suggest that the ASi particulate load is much greater than previously believed, rivaling that of the DSi load with important implications for the global Si cycle and oceanic Si isotopic budget

Bacterial and fungal colonization and decomposition of submerged plant litter: consequences for biogenic silica dissolution.

We studied bacterial and fungal colonization of submerged plant litter, using a known Si-accumulator (Equisetum arvense), in experimental microcosms during one month. We specifically addressed the microbial decomposer role concerning biogenic silica (bSiO2) dissolution from the degrading litter. To vary the rates and level of microbial colonization, the litter was combined with a range of mineral nitrogen (N) and phosphorous (P) supplements. Overall microbial growth on plant litter increased with higher levels of N and P. There was a tendency for higher bacterial than fungal stimulation with higher nutrient levels. Differences in microbial colonization of litter between treatments allowed us to test how Si remineralization from plants was influenced by microbial litter decomposition. Contrary to previous results and expectations, we observed a general reduction in Si release from plant litter colonized by a microbial community, compared with sterile control treatments. This suggested that microbial growth resulted in a reduction in dissolved Si concentrations, and we discuss candidate mechanisms to explain this outcome. Hence, our results imply that the microbial role in plant litter associated Si turnover is different from that commonly assumed based on bSiO2 dissolution studies in aquatic ecosystems