Determining tributary sources of increased sedimentation in East-African Rift Lakes.

Temporal and spatial sediment dynamics in an East-African Rift Lake (Lake Manyara, Tanzania), and its river inputs, have been evaluated via a combination of sediment tracing and radioactive dating. Changes in sedimentation rates were assessed using radioactive dating of sediment cores in combination with geochemical profile analysis of allogenic and autogenic elements. Geochemical fingerprinting of riverine and lake sediment was integrated within a Bayesian mixing model framework, including spatial factors, to establish which tributary sources were the main contributors to recent lake sedimentation. The novel application of Bayesian source attribution on sediment cores and subsequent integration with sedimentation data permitted the coupling of changes in the rate of lake sedimentation with variations in sediment delivery from the tributaries. These complimentary evidence bases demonstrated that Lake Manyara has experienced an overall upward trajectory in sedimentation rates over the last 120 years with distinct maxima between 0.80 and 0.85 g cm-2 yr-1 in the 1960s and between 0.84 and 1.81 g cm-2 yr-1 in 2010. Increased sedimentation rates are largely a result of a complex interaction between increased upstream sediment delivery following changes in land cover and natural rainfall fluctuations. Modelling results identified two specific tributaries as responsible for elevated sedimentation rates, contributing 58% and 38% of the recently deposited lake sediment. However, the effects of sedimentation were shown to be spatially distinct given the domination of different tributaries in various areas of Lake Manyara. The application of source-tracing techniques constrained sedimentation problems in Lake Manyara to specific tributary sources and established a link between upstream land degradation and downstream ecosystem health. This novel application provides a solid foundation for targeted land and water management strategies to safeguard water security and environmental health in Lake Manyara and has potential application to fill knowledge gaps on sediment dynamics in other East-African Rift Lakes.

River rehabilitation for the delivery of multiple ecosystem services at the river network scale.

This paper presents a conceptual framework and methodology to assist with optimising the outcomes of river rehabilitation in terms of delivery of multiple ecosystem services and the benefits they represent for humans at the river network scale. The approach is applicable globally, but was initially devised in the context of a project critically examining opportunities and constraints on delivery of river rehabilitation in Scotland. The spatial-temporal approach highlighted is river rehabilitation measure, rehabilitation scale, location on the stream network, ecosystem service and timescale specific and could be used as initial scoping in the process of planning rehabilitation at the river network scale. The levels of service delivered are based on an expert-derived scoring system based on understanding how the rehabilitation measure assists in reinstating important geomorphological, hydrological and ecological processes and hence intermediate or primary ecosystem function. The framework permits a "total long-term (>25 years) ecosystem service score" to be calculated which is the cumulative result of the combined effect of the number of and level of ecosystem services delivered over time. Trajectories over time for attaining the long-term ecosystem service score for each river rehabilitation measures are also given. Scores could also be weighted according to societal values and economic valuation. These scores could assist decision making in relation to river rehabilitation at the catchment scale in terms of directing resources towards alternative scenarios. A case study is presented of applying the methodology to the Eddleston Water in Scotland using proposed river rehabilitation options for the catchment to demonstrate the value of the approach. Our overall assertion is that unless sound conceptual frameworks are developed that permit the river network scale ecosystem services of river rehabilitation to be evaluated as part of the process of river basin planning and management, the total benefit of river rehabilitation may well be reduced. River rehabilitation together with a 'vision' and framework within which it can be developed, is fundamental to future success in river basin management.

Using remote sensing to aid the assessment of human health risks from blooms of potentially toxic cyanobacteria.

Mass populations of toxic cyanobacteria in recreational waters can present a serious risk to human health. Intelligence on the abundance and distribution of cyanobacteria is therefore needed to aid risk assessment and management activities. In this paper, we use data from the Compact Airborne Spectrographic Imager-2 (CASI-2) to monitor seasonal change in the concentration of chlorophyll a (Chl a) and the cyanobacterial biomarker pigment C-phycocyanin (C-PC) in a series of shallow lakes in the U.K. The World Health Organization guidance levels for cyanobacteria in recreational waters were subsequently used to build a decision tree classification model for cyanobacterial risk assessment which was driven using Chl a and C-PC products derived from the CASI-2 data. The results demonstrate that remote sensing can be used to acquire intelligence on the distribution and abundance of cyanobacteria in inland waterbodies. It is argued the use of remote sensing reconnaissance, in conjunction with in situ based monitoring approaches, would greatly aid the assessment of cyanobacterial risks in inland waters and improve our ability to protect human health.