Giamba Bussi and colleagues have used INCA model to develop a decision support system to assess water quality impacts in urban rivers. Poor water quality is a widespread issue in urban rivers and streams throughout the world. Localised pollution can have impacts on local communities, from health issues to environmental degradation and restricted recreational use of water. The Salmons and Pymmes Brooks, located in London UK, have significant pollution impacts from misconnected sewers, urban runoff and atmospheric pollution. The first step towards finding sustainable and effective solutions to these issues is to identify sources and paths of pollutants and to understand their cycle through catchments and rivers. The team applied INCA to the two urban catchments with the aim of providing local communities and community action groups such as Thames21 with a tool they can use to assess the water quality issue. They evaluated a set of mitigation strategies including constructed wetland across the catchment to assess pollution control. Constructed wetlands can make a significant difference reducing sediment transport and improving nutrient control for nitrogen and phosphorus. This study showed that a substantial reduction in nitrate, ammonium and phosphorus concentrations can be achieved if a proper catchment-scale wetland implementation strategy is put in place. Furthermore, nutrient reduction efficiency of the wetlands should not be affected by climate change.
Future patterns of streamflow are likely to be a primary driver of aquatic ecology. Using rainflow runoff models such as PERSiST may be one way to evaluate the possible impacts of climate change and land management on the ecology of vulnerable aquatic species. José Ledesma and colleagues published such a study to evaluate future habitat availability the the Montseny brook newt (Calotriton arnoldi). They concluded that future low streamflow conditions will likely pose a severe threat for the survival of the Montseny brook newt but appropriate local management actions including limiting the expansion of holm oak forest may increase the chances for species survival.
The Montseny brook newt is a critically endangered amphibian species which inhabits a small 20 km2 holm oak and beech forest area in northeast Spain. The species can only live in running waters and might be highly vulnerable to hydrological perturbations such as increased drought frequency that could occur under climate and vegetation cover changes. Scenarios describing potential changes in species habitat due to global and local environmental changes can help identify and prioritize the actions needed for its conservation. Based on knowledge of the species and supported by observations, José Ledesma and colleagues proposed daily low and high streamflow event thresholds for the viability of the species. They used PERSiST to simulate changes in the frequency and duration of streamflow events under two climate and four vegetation cover scenarios for near-future (2031–2050) and far-future (2081–2100) periods in a reference catchment. All future scenarios projected a significant decrease in annual streamflow (between 21% and 67%) with respect to the reference period. The frequency and length of low streamflow events was also projected to dramatically increase. In contrast, the risk of catastrophic drift linked to flash floods was projected to decrease. Local hydrologcial effects associated with a potential change in vegetation toward an expansion of holm oak forests will likely be more important than climate changes in determining threshold low flow conditions. This indicates that consideration of both local (potential changes in vegetation) and global (temperature and precipitation) is essential in simulating future aquatic habitats.
Shanta Sharma recently defended her Masters thesis on modelling dissolved organic carbon (DOC) in the Canadian sub-Arctic. This was one of the most northerly applications of the INCA family of models and brought some unique challenges and insights.
The sub-Arctic in Canada and elsewhere is likely to experience hydroclimatic regime change associated with a rapidly changing climate. Simulations of landscape-scale carbon (C) budgets and pollutant transfer are needed by northern managers and stakeholders to understand and mitigate these possible impacts. The project simulated dissolved organic carbon (DOC) fluxes in a hydrologically complex watershed (Baker Creek) in the Northwest Territories. Discharge, DOC concentration, and DOC export were simulated PERSiST and INCA-C. The models were calibrated against available (2012-2016) discharge and DOC concentration data in sub-catchments of Baker Creek. The model successfully reproduced flow (R2: 0.87–0.94; NS: 0.82–0.91) and captured some aspects of DOC concentration dynamics (R2: 0.19–0.31).
Possible future conditions were simulated using two climate scenarios (elevated temperature (T), elevated temperature and precipitation (T+P)), and compared against a baseline scenario. Average discharge is projected to decrease under scenario T (22–27% of baseline) and increase (116–175% of baseline) under the T+P scenario. In this scenario, early winter increases in discharge suggest a change in hydroclimatic regime from nival to combined nival and pluvial. Future DOC fluxes are projected to decrease (24–27% of baseline) under scenario T and increase (64–81% of baseline) in the T+P scenario, with much of the increase in DOC export occurring during early winter. Any future increase in DOC export from Baker Creek may increase the mobility of previously deposited airborne metal contaminants, e.g., arsenic from Giant Mine.
Petr Kupec and colleagues have published a new paper about possible future hydrological regime shifts in Central European forests. They used long-term data, detailed field measurements from an experimental forest catchent and PERSiST modelling, we show that there is a prolonged and persistent decline in annual runoff:precipitation ratios. This decline is most likely linked to the longer growing seasons associated with global warming. They performed a long term (1950–2018) water balance simulation for a Czech upland forest headwater catchment calibrated against measured streamflow and transpiration from deciduous and coniferous stands. Their simulations were corroborated by long-term (1965–2018) borehole measurements and historical drought reports. A regime shift from positive to negative catchment water balances likely occurred in the early part of this century. Since 2007, annual runoff:precipitation ratios have been below the long-term average. Notably, annual average temperatures have increased, but there have been no notable long term trends in precipitation. Since 1980, there has been a pronounced April warming, likely leading to earlier leaf out and higher annual transpiration, making water unavailable for runoff generation and/or soil moisture recharge. Their results suggest a regime shift due to second order effects of climate change where increased transpiration associated with a longer growing season leads to a shift from light to water limitation in central European forests. If their finding can be generalized, it will require new approaches to managing forests where water limitation has previously not been a problem.
Climate change may alter the services ecosystems provide by changing ecosystem functioning. As ecosystems can also resist environmental perturbations, it is crucial to consider the different processes that influence resilience. “Climate proofing” can identify potential climate-related threats to ongoing delivery of ecosystem services. Dr. Katri Rankinen and colleagues have published a new study modelling the potential for increased nitrate(NO3−) concentrations in drinking water due to climate change. They analyzed catchment-scale changes in ecosystem services connected to water purification in southern Finland by combining climate change scenarios with process-based forest growth (PREBAS) and eco-hydrological (PERSiST and INCA) models. By using the aforementioned model chain, they improved traditional model calibration by including timing of forest phenology and duration of the snow-covered period from networks of cameras and satellite data. They upscaled the combined modelling results with scenarios of population growth to produce vulnerability maps. Their results show that boreal ecosystems seemed to be strongly buffered against increased NO3– leaching by a combination of increases in evapotranspiration and vegetation NO3– uptake. Societal vulnerability varied greatly between scenarios and municipalities. The most vulnerable areas were agricultural regions on permeable soil types.
Dr. Jan Deutscher and colleagues present a new study modelling streamflow decline in the Central European uplands. This study is timely as in recent decades the effects of global climate change have caused a continuous drying out of temperate landscapes. In Czech forests, this drying out has been manifested as a visible decrease in streamflow. Dr. Deutscher and colleagues address questions related to the severity of the streamflow decrease and attempt to identify its main causes. They base their analysis on daily streamflow, temperature, and precipitation data measured during five years (1/11/2014 to 31/10/2019) in a spruce-dominated temperate upland catchment located in the Czech Republic. Streamflow values were modeled in with PERSiST using precipitation and temperature values obtained from the observational E-OBS gridded dataset and calibrated against in situ measured discharge. Their modeling results show a greater than 65% decline in streamflow during the five-year study period at the Křtiny experimental catchment. This trend is most likely caused by increasing temperature. They found a strong relationship between increasing temperature and decreasing discharge during the growing seasons, which can be simplified to an increasing trend in the mean daily temperature of 0.1o C per season, effectively causing a decreasing trend in the discharge of −10% per season regardless of the increasing precipitation during the period.
Maria Holmberg and colleagues present an approach to collate spatially explicit estimated fluxes of GHGs (carbon dioxide, methane and nitrous oxide) for the main land use sectors in the landscape, and show how these fluxes can be aggregated to calculate net emissions of an entire region. They used INCA-C and PERSiST to estimate the flux of organic carbon from terrestrial ecosystems to lakes and rivers.
They developed and tested the approach in a large river basin in Finland, providing information from intensively studied eLTER research sites. To evaluate the full GHG balance, they included fluxes from natural ecosystems (lakes, rivers, and undrained mires) together with anthropogenic fluxes from agriculture and forestry. They quantified fluxes using an anthropogenic emissions model (FRES), a forest growth and carbon balance model (PREBAS), and literature values for emissions from lakes, rivers, undrained mires, peat extraction sites and cropland. Spatial data sources included CORINE land use data, soil map, lake and river shorelines, national forest inventory data, and statistical data on anthropogenic activities. Emission uncertainties were evaluated with Monte Carlo simulations. They summed the vertical fluxes of spatially explicit net emissions, disregarding the impact of lateral fluxes from terrestrial to aquatic ecosystems on the vertical fluxes.
Their model results showed that artificial surfaces were the most emission intensive land-cover class while lakes and rivers were about as emission intensive as arable land. Forests were the dominant land cover in the region (66%). The forest C sink decreased total emissions for the region by 72%. The region’s net emissions amounted to 4.37 ± 1.43 Tg CO2-eq yr-1, corresponding to a net emission intensity 0.16 Gg CO2-eq km-2 yr-1, and estimated per capita net emissions of 5.6 Mg CO2-eq yr-1. Using INCA-C and PERSiST, the amount of organic C leaching from mires, cropland, and forests to the watercourses was estimated to correspond to about 10% of the CO2 and CH4 emissions from land to air.
Although the landscape approach developed by Dr. Holmberg and colleagues opens opportunities to examine the sensitivities of important GHG fluxes to changes in land use and climate, management actions, and mitigation of anthropogenic emissions, there is still a need to extend the work to a fully integrated regional GHG budget, accounting for all lateral fluxes of C- and N-containing compounds.
Giamba Bussi and colleagues have published a new study of the effects that dams and climate change are having on sediment transport in the Mekong Delta. Credible predictions of sediment dynamics are essential for achieving the UN Sustainable Development Goals. The livelihoods of millions of people living in the world’s deltas are deeply interconnected with the sediment dynamics of these deltas. Sustainable inputs of fluvial sediments from upstream rivers are 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, Dr. Bussi and colleagues apply the INCA hydrological and sediment model to the Mekong River catchment in South East Asia. Their aim was to assess the impact of several large dams (both existing and planned) on suspended sediment fluxes in the river. After calibrating to present day conditions, they forced the INCA model with future climate scenarios to assess the interplay of changing climate and sediment trapping caused by dam construction. Their results suggest that historical sediment flux declines have mostly been caused by dam construction and that sediment trapping will increase in the future if new, planed dams are constructed. If all dams that are currently planned for the next two decades are built, the model predicts a decline of suspended sediment flux of 50% (47–53% 90% confidence interval) compared to current levels (99 Mt/year at the delta apex), with potentially damaging consequences for local livelihoods and ecosystems.
Paul Whitehead and colleagues have published a new version of INCA. INCA-Metals, to simulate the impact of point source metal discharges (e.g., from tannery wastes or acid mine drainage) and diffuse rural runoff on riverine water quality. The model accounts for the key chemical reaction kinetic processes operating as well as sedimentation, resuspension, dilution, mixing and redistribution of pollutants in rivers downstream of discharge points. The model is dynamic and simulates the daily hydrology and behavior of eight metals, including cadmium, mercury, copper, zinc, lead, arsenic, manganese and chromium, as well as cyanide and ammonia. Like all members of the INCA family, the model is semi-distributed and can simulate catchment, tributary and instream river behavior. The apply the new model to predict impacts of the Savar tannery complex on the Dhaleshwari River system in Bangladesh on pollution levels in the river system and to evaluate a set of treatment scenarios for pollution control, particularly in the dry season. They show that the new efﬂuent treatment plant at Savar needs to signiﬁcantly improve its operation and treatment capability in order to alleviate metal pollution in the downstream Dhaleshwari River System and also protect the Meghna River System that discharges into the Bay of Bengal.
Paul Whitehead and colleagues have published a new study of microplastics in the Thames River, UK. This is an exciting paper for a number of reasons. It is one of the first realistic applications of a riverine water quality model to the problem of microplastic pollution and it is the first published paper using the INCA-Microplastics model with real data. This study also presents one of the first examples of an INCA model implemented using the open source MOBIUS framework.
Microplastic pollution of surface waters is an issue of increasing societal concern. Plastics and microplastics are ubiquitous in freshwater ecosystems. Understanding the transport and distribution of microplastics in river systems is key to assessing impacts. Modelling the main flow dynamics, mixing, sedimentation and resuspension processes is essential for an understanding of the transport processes. Professor Whitehead and colleagues applied INCA-Microplastics to the whole of the freshwater catchment of the River Thames, UK, to evaluate inputs, loads and concentrations along the river system. They calibrated the model against UK water industry measurements of microplastics in effluent discharges and sewage sludge. In their simulation, they showed significant increases in microplastic loads moving along the river system, with rising concentrations in downstream reaches and increasing deposition to the riverbed. The paper presents an assessment of potential impacts on aquatic ecosystems and a review of policy implications.