Modelling fixed plant and algal dynamics in rivers: an application to the River Frome

The development of eutrophication in river systems is poorly understood given the complex relationship between fixed plants, algae, hydrodynamics, water chemistry and solar radiation. However there is a pressing need to understand the relationship between the ecological status of rivers and the controlling environmental factors to help the reasoned implementation of the Water Framework Directive and Catchment Sensitive Farming in the UK. This research aims to create a dynamic, process-based, mathematical in-stream model to simulate the growth and competition of different vegetation types (macrophytes, phytoplankton and benthic algae) in rivers. The model, applied to the River Frome (Dorset, UK), captured well the seasonality of simulated vegetation types (suspended algae, macrophytes, epiphytes, sediment biofilm). Macrophyte results showed that local knowledge is important for explaining unusual changes in biomass. Fixed algae simulations indicated the need for the more detailed representation of various herbivorous grazer groups, however this would increase the model complexity, the number of model parameters and the required observation data to better define the model. The model results also highlighted that simulating only phytoplankton is insufficient in river systems, because the majority of the suspended algae have benthic origin in short retention time rivers. Therefore, there is a need for modelling tools that link the benthic and free-floating habitats

Dynamic response of land use and river nutrient concentration to long-term climatic changes

The combined indirect and direct impacts of land use change and climate change on river water quality were assessed. A land use allocation model was used to evaluate the response of the catchment land use to long-term climatic changes. Its results were used to drive a water quality model and assess the impact of climatic alterations on freshwater nitrate and phosphorus concentrations. Climatic projections were employed to estimate the likelihood of such response. The River Thames catchment (UK) was used as a case-study. If land use is considered as static parameter, according to the model results, climate change alone should reduce the average nitrate concentration, although just by a small amount, by the 2050s in the Lower Thames, due to reduced runoff (and lower export of nitrate from agricultural soils) and increased instream denitrification, and should increase the average phosphorus concentration by 12% by the 2050s in the Lower Thames, due to a reduction of the effluent dilution capacity of the river flow. However, the results of this study also show that these long-term climatic alterations are likely to lead to a reduction in the arable land in the Thames, replaced by improved grassland, due to a decrease in agriculture profitability in the UK. Taking into account the dynamic co-evolution of land use with climate, the average nitrate concentration is expected to be decreased by around 6% by the 2050s in both the upper and the lower Thames, following the model results, and the average phosphorus concentration increased by 13% in the upper Thames and 5% in the lower Thames. On the long term (2080s), nitrate is expected to decrease by 9% and 8% (upper and lower Thames respectively) and phosphorus not to change in the upper thames and increase by 5% in the lower Thames

Assessment of risks to public water supply from low flows and harmful water quality in a changing climate

Water resources planning and management by water utilities have traditionally been based on consideration of water availability. However, the reliability of public water supplies can also be influenced by the quality of water bodies. In this study, we proposed a framework that integrates the analysis of risks of inadequate water quality and risks of insufficient water availability. We have developed a coupled modeling system that combines hydrological modeling of river water quantity and quality, rules for water withdrawals from rivers into storage reservoirs, and dynamical simulation of harmful algal blooms in storage reservoirs. We use this framework to assess the impact of climate change, demand growth, and land‐use change on the reliability of public water supplies. The proposed method is tested on the River Thames catchment in the south of England. The results show that alongside the well‐known risks of rising water demand in the south of England and uncertain impacts of climate change, diffuse pollution from agriculture and effluent from upstream waste water treatment works potentially represent a threat to the reliability of public water supplies in London. We quantify the steps that could be taken to ameliorate these threats, though even a vigorous pollution‐prevention strategy would not be sufficient to offset the projected effects of climate change on water quality and the reliability of public water supplies. The proposed method can help water utilities to recognize their system vulnerability and evaluate the potential solutions to achieve more reliable water supplies. supplie

Long-term predictions of ecosystem acidification and recovery

This paper considers the long-term (500 year) consequences of continued acid deposition, using a small forested catchment in S. England as an example. The MAGIC acidification model was calibrated to the catchment using data for the year 2000, and run backwards in time for 200 years, and forwards for 500. Validation data for model predictions were provided by various stream and soil measurements made between 1977 and 2013. The model hindcast suggests that pre-industrial stream conditions were very different from those measured in 2000. Acid Neutralising Capacity (ANC) was +150 μeq L−1 and pH 7.1: there was little nitrate (NO3). By the year 2000, acid deposition had reduced the pH to 4.2 and ANC to c. −100 μeq L−1, and NO3 was increasing in the stream. The future state of the catchment was modelled using actual deposition reductions up to 2013, and then based on current emission reduction commitments. This leads to substantial recovery, to pH 6.1, ANC +43 μeq L−1, though it takes c. 250 years. Then, however, steady acidification resumes, due to continued N accumulation in the catchment and leaching of NO3. Soil data collected using identical methods in 1978 and 2013 show that MAGIC correctly predicts the direction of change, but the observed data show more extreme changes – reasons for this are discussed. Three cycles of forest growth were modelled – this reduces NO3 output substantially during the active growth phase, and increases stream pH and ANC, but acidifies the soil which continues to accumulate nitrogen. The assumptions behind these results are discussed, and it is concluded that unmanaged ecosystems will not return to a pre-industrial state in the foreseeable future

Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK)

Potential increases of phytoplankton concentrations in river systems due to global warming and changing climate could pose a serious threat to the anthropogenic use of surface waters. Nevertheless, the extent of the effect of climatic alterations on phytoplankton concentrations in river systems has not yet been analysed in detail. In this study, we assess the impact of a change in precipitation and temperature on river phytoplankton concentration by means of a physically-based model. A scenario-neutral methodology has been employed to evaluate the effects of climate alterations on flow, phosphorus concentration and phytoplankton concentration of the River Thames (southern England). In particular, five groups of phytoplankton are considered, representing a range of size classes and pigment phenotypes, under three different land-use/land-management scenarios to assess their impact on phytoplankton population levels. The model results are evaluated within the framework of future climate projections, using the UK Climate Projections 09 (UKCP09) for the 2030s. The results of the model demonstrate that an increase in average phytoplankton concentration due to climate change is highly likely to occur, with the magnitude varying depending on the location along the River Thames. Cyanobacteria show significant increases under future climate change and land use change. An expansion of intensive agriculture accentuates the growth in phytoplankton, especially in the upper reaches of the River Thames. However, an optimal phosphorus removal mitigation strategy, which combines reduction of fertiliser application and phosphorus removal from wastewater, can help to reduce this increas

From paradox to pattern shift: Conceptualising liminal hotspots and their affective dynamics

This article introduces the concept of liminal hotspots as a specifically psychosocial and sociopsychological type of wicked problem, best addressed in a process-theoretical framework. A liminal hotspot is defined as an occasion characterised by the experience of being trapped in the interstitial dimension between different forms-of-process. The paper has two main aims. First, to articulate a nexus of concepts associated with liminal hotspots that together provide general analytic purchase on a wide range of problems concerning “troubled” becoming. Second, to provide concrete illustrations through examples drawn from the health domain. In the conclusion, we briefly indicate the sense in which liminal hotspots are part of broader and deeper historical processes associated with changing modes for the management and navigation of liminality

Biogenic cloud nuclei in the central Amazon during the transition from wet to dry season

© Author(s) 2016. This work is distributed under the Creative Commons Attribution 3.0 License. Whitehead, J. D., Darbyshire, E., Brito, J., Barbosa, H. M. J., Crawford, I., Stern, R., Gallagher, M. W., Kaye, P. H., Allan, J. D., Coe, H., Artaxo, P., and McFiggans, G.: Biogenic cloud nuclei in the central Amazon during the transition from wet to dry season, Atmos. Chem. Phys., 16, 9727-9743, doi:10.5194/acp-16-9727-2016, 2016.The Amazon basin is a vast continental area in which atmospheric composition is relatively unaffected by anthropogenic aerosol particles. Understanding the proper- ties of the natural biogenic aerosol particles over the Ama- zon rainforest is key to understanding their influence on re- gional and global climate. While there have been a number of studies during the wet season, and of biomass burning par- ticles in the dry season, there has been relatively little work on the transition period – the start of the dry season in the absence of biomass burning. As part of the Brazil–UK Net- work for Investigation of Amazonian Atmospheric Composi- tion and Impacts on Climate (BUNIAACIC) project, aerosol measurements, focussing on unpolluted biogenic air masses, were conducted at a remote rainforest site in the central Ama- zon during the transition from wet to dry season in July 2013. This period marks the start of the dry season but before sig- nificant biomass burning occurs in the region. Median particle number concentrations were 266 cm−3, with size distributions dominated by an accumulation mode of 130–150 nm. During periods of low particle counts, a smaller Aitken mode could also be seen around 80 nm. While the concentrations were similar in magnitude to those seen during the wet season, the size distributions suggest an en- hancement in the accumulation mode compared to the wet season, but not yet to the extent seen later in the dry sea- son, when significant biomass burning takes place. Submi- cron nonrefractory aerosol composition, as measured by an aerosol chemical speciation monitor (ACSM), was domi- nated by organic material (around 81 %). Aerosol hygro- scopicity was probed using measurements from a hygro- scopicity tandem differential mobility analyser (HTDMA), and a quasi-monodisperse cloud condensation nuclei counter (CCNc). The hygroscopicity parameter, κ , was found to be low, ranging from 0.12 for Aitken-mode particles to 0.18 for accumulation-mode particles. This was consistent with pre- vious studies in the region, but lower than similar measure- ments conducted in Borneo, where κ ranged 0.17–0.37. A wide issue bioaerosol sensor (WIBS-3M) was deployed at ground level to probe the coarse mode, detecting pri- mary biological aerosol by fluorescence (fluorescent biolog- ical aerosol particles, or FBAPs). The mean FBAP number concentration was 400 ± 242 L−1; however, this ranged from around 200 L−1 during the day to as much as 1200 L−1 at night. FBAPs dominated the coarse-mode particles, compris- ing between 55 and 75 % of particles during the day to more than 90 % at night. Non-FBAPs did not show a strong diur- nal pattern. Comparison with previous FBAP measurements above canopy at the same location suggests there is a strong vertical gradient in FBAP concentrations through the canopy. Cluster analysis of the data suggests that FBAPs were dom- inated (around 70 %) by fungal spores. Further, long-term measurements will be required in order to fully examine the seasonal variability and distribution of primary biological aerosol particles through the canopy. This is the first time that such a suite of measurements has been deployed at this site to investigate the chemical compo- sition and properties of the biogenic contributions to Ama- zonian aerosol during the transition period from the wet to the dry season, and thus provides a unique comparison to the aerosol properties observed during the wet season in previ- ous similar campaigns. This was also the first deployment of a WIBS in the Amazon rainforest to study coarse-mode parti- cles, particularly primary biological aerosol particles, which are likely to play an important role as ice nuclei in the region.Peer reviewe

Impact of dams and climate change on suspended sediment flux to the Mekong delta

The livelihoods of millions of people living in the world's deltas are deeply interconnected with the sediment dynamics of these deltas. In particular a sustainable supply of fluvial sediments from upstream is critical for ensuring the fertility of delta soils and for promoting sediment deposition that can offset rising sea levels. Yet, in many large river catchments this supply of sediment is being threatened by the planned construction of large dams. In this study, we apply the INCA hydrological and sediment model to the Mekong River catchment in South East Asia. The aim is to assess the impact of several large dams (both existing and planned) on the suspended sediment fluxes of the river. We force the INCA model with a climate model to assess the interplay of changing climate and sediment trapping caused by dam construction. The results show that historical sediment flux declines are mostly caused by dams built in PR China and that sediment trapping will increase in the future due to the construction of new dams in PDR Lao and Cambodia. If all dams that are currently planned for the next two decades are built, they will induce a decline of suspended sediment flux of 50% (47–53% 90% confidence interval (90%CI)) compared to current levels (99 Mt/year at the delta apex), with potentially damaging consequences for local livelihoods and ecosystems

Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK)

Potential increases of phytoplankton concentrations in river systems due to global warming and changing climate could pose a serious threat to the anthropogenic use of surface waters. Nevertheless, the extent of the effect of climatic alterations on phytoplankton concentrations in river systems has not yet been analysed in detail. In this study, we assess the impact of a change in precipitation and temperature on river phytoplankton concentration by means of a physically-based model. A scenario-neutral methodology has been employed to evaluate the effects of climate alterations on flow, phosphorus concentration and phytoplankton concentration of the River Thames (southern England). In particular, five groups of phytoplankton are considered, representing a range of size classes and pigment phenotypes, under three different land-use/land-management scenarios to assess their impact on phytoplankton population levels. The model results are evaluated within the framework of future climate projections, using the UK Climate Projections 09 (UKCP09) for the 2030s. The results of the model demonstrate that an increase in average phytoplankton concentration due to climate change is highly likely to occur, with the magnitude varying depending on the location along the River Thames. Cyanobacteria show significant increases under future climate change and land use change. An expansion of intensive agriculture accentuates the growth in phytoplankton, especially in the upper reaches of the River Thames. However, an optimal phosphorus removal mitigation strategy, which combines reduction of fertiliser application and phosphorus removal from wastewater, can help to reduce this increase in phytoplankton concentration, and in some cases, compensate for the effect of rising temperature