A deterministic evaluation analysis applied to an integrated soil-crop model

A Comprehensive Evaluation Model of Ammonia Pollution Trends in a Groundwater Source Area along a River in Residential Areas

In this study, a comprehensive evaluation model of ammonia pollution trends in a groundwater source area along a river in residential areas is proposed. It consists of coupling models and their interrelated models, including (i) MODFLOW and (ii) MT3DMS. The study area is laid in a plain along a river, where a few workshops operate and groundwater is heavily contaminated by domestic pollutants, agricultural pollutants, and cultivation pollutants. According to the hydrogeological conditions of the study area and the emissions of ammonia calculated in the First National Pollution Source Census Report in China, this study calibrates and verifies the prediction model. The difference between the observed water level and the calculated water level of the model is within the confidence interval of the test. This means that the model is reliable and that it can truly reflect changes in the groundwater flow field and can be directly used to simulate the migration of ammonia. The simulation results show that, after 20 years, the center of the ammonia pollution plume will gradually flow east along with the groundwater over time, mainly affecting the groundwater, which is less than 200 m from the river, and the ammonia content near wells at a maximum extent of less than 0.3 mg/L.

Review of scenario analyses to reduce agricultural nitrogen and phosphorus loading to the aquatic environment

Nutrient loadings of nitrogen (N) and phosphorus (P) to aquatic environments are of increasing concern globally for managing ecosystems, drinking water supply and food production. There are often multiple sources of these nutrients in the landscape, and the different hydrological flow patterns within stream or river catchments have considerable influence on nutrient transport, transformation and retention processes that all eventually affect loadings to vulnerable aquatic environments. Therefore, in order to address options to reduce nutrient loadings, quantitative assessment of their effects in real catchments need to be undertaken. This involves setting up scenarios of the possible nutrient load reduction measures and quantifying their impacts via modelling. Over the recent two decades there has been a great increase in the use of scenario-based analyses of strategies to combat excessive nutrient loadings. Here we review 130 published papers extracted from Web of Science for 1995 to 2014 that have applied models to analyse scenarios of agricultural impacts on nutrients loadings at catchment scale. The review shows that scenario studies have been performed over a broad range of climatic conditions, with a large focus on measures targeting land cover/use and land management for reducing the source load of N and P in the landscape. Some of the studies considered how to manage the flows of nutrients, or how changes in the landscape may be used to influence both flows and transformation processes. Few studies have considered spatially targeting measures in the landscape, and such studies are more recent. Spatially differentiated options include land cover/use modification and application of different land management options based on catchments characteristics, cropping conditions and climatic conditions. Most of the studies used existing catchment models such as SWAT and INCA, and the choice of the models may also have influenced the setup of the scenarios. The use of stakeholders for designing scenarios and for communication of results does not seem to be a widespread practice, and it would be recommendable for future scenario studies to have a more in-depth involvement of stakeholders for the elaboration and interpretation of scenarios, in particular to enhance their relevance for farm and catchment management and to foster better policies and incentives.

Nitrate dynamics in agricultural catchments deduced from groundwater dating and long-term nitrate monitoring in surface- and groundwaters

Although nitrate export in agricultural catchments has been simulated using various types of models, the role of groundwater in nitrate dynamics has rarely been fully taken into account. We used groundwater dating methods (CFC analyses) to reconstruct the original nitrate concentrations in the groundwater recharge in Brittany (Western France) from 1950 to 2009. This revealed a sharp increase in nitrate concentrations from 1977 to 1990 followed by a slight decrease. The recharge concentration curve was then compared with past chronicles of groundwater concentration. Groundwater can be interpreted as resulting from the annual dilution of recharge water in an uncontaminated aquifer. Two aquifers were considered: the weathered aquifer and the deeper fractured aquifer. The nitrate concentrations observed in the upper part of the weathered aquifer implied an annual renewal rate of 27 to 33% of the reservoir volume while those in the lower part indicated an annual renewal rate of 2-3%. The concentrations in the deep fractured aquifer showed an annual renewal rate of 0.1%. The river concentration can be simulated by combining these various groundwater reservoirs with the recharge. Winter and summer waters contain i) recharge water, or water from the variably saturated zone with rapid transfer and high nitrate concentrations, and ii) a large contribution (from 35 to 80% in winter and summer, respectively) from the lower part of the aquifer (lower weathered aquifer and deep fractured aquifer). This induces not only a relatively rapid response of the catchment to variations in agricultural pressure, but also a potential inertia which has to be taken into account.

Assessment of Evapotranspiration and Soil Moisture Content Across Different Scales of Observation

The proper assessment of evapotranspiration and soil moisture content are fundamental in food security research, land management, pollution detection, nutrient flows, (wild-) fire detection, (desert) locust, carbon balance as well as hydrological modelling; etc. This paper takes an extensive, though not exhaustive sample of international scientific literature to discuss different approaches to estimate land surface and ecosystem related evapotranspiration and soil moisture content. This review presents: (i)

a summary of the generally accepted cohesion theory of plant water uptake and transport including a shortlist of meteorological and plant factors influencing plant transpiration;

(ii)

a summary on evapotranspiration assessment at different scales of observation (sap-flow, porometer, lysimeter, field and catchment water balance, Bowen ratio, scintillometer, eddy correlation, Penman-Monteith and related approaches);

(iii)

a summary on data assimilation schemes conceived to estimate evapotranspiration using optical and thermal remote sensing; and

(iv)

for soil moisture content, a summary on soil moisture retrieval techniques at different spatial and temporal scales is presented.

Concluding remarks on the best available approaches to assess evapotranspiration and soil moisture content with and emphasis on remote sensing data assimilation, are provided.