University of Twente Student Theses


Predicting the effect of reducing the nutrient surplus on the nutrient drainage in the province of Fryslân

Mossink, A.S. (2016) Predicting the effect of reducing the nutrient surplus on the nutrient drainage in the province of Fryslân.

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Abstract:The water quality in the water bodies of the province of Fryslân is insufficient according to the requirements of the water framework directive (WFD). To improve the water quality in Fryslân, wetterskip Fryslân and AlterraWageningenUR are investigating measures, that can be applied on a local level, like a farm, to decrease the nutrient drainage1. This research in specific, investigates the influence of decreasing the nutrient surplus2 on the nutrient drainage to the waterbodies from the grasslands in the province of Fryslân. Different examinations are executed for the effects of nitrogen and phosphorus, furthermore datasets are divided into data collected at sandy soils and data collected at clay soils. With the results from the examination a tool will be developed. A tool that is able to quickly predict the effect of decreasing the nutrient surplus in a specific area. First, literature study is done, to understand the nutrient cycle. Using literature, different factors that determine the nutrient drainage are found. The statistical significance of the influence of these factors are analysed, with a t-test and a correlation study. At hand of the t-test, the correlation study and the literature study the factors are combined and filtered from the dataset. With the remaining datasets, multiple regression analyses are done. For each dataset an analysis is done that takes into account nominal and numerical variables and one is done that takes into account only numerical values. Furthermore, for sandy soils the dataset is divided in sub-datasets with a certain characteristic of the dataset, for instance: irrigation is present. This sub-dataset is aimed to find more precise relations between the nutrient drainage and the nutrient surplus for areas that share the same characteristics. In the last step predictions are made for decreasing the nutrient surplus is sandy soils with 5%. The effect of such a reduction on the nutrient drainage is calculated. An important aspect of all the equations obtained from the multiple regression analysis is the validation and verification. To make predictions with the obtained equations, it is useful to address the uncertainties. Therefore, the equation is validated on: its linearity, its correlation coefficient, the error, the variables and parameters involved, the best fit with the original dataset and the possible indications of overfitting. The most accurate and probable equations that are derived from the multiple regression analyses are used for prediction making. The regression analyses for nitrogen do show a valid relation between the nitrogen surplus and the nitrogen drainage. Decreasing the nutrient surplus with 5% causes a decrease of the nutrient drainage in range of 0.67-5.26%. The obtained equations can be used to make predictions, however improvements can be made. This research suggests that, taking into consideration bigger datasets, considering more specified data and involving other variables like: average highest groundwater level or the storage of nutrients in the soil, can improve the accuracy of the regression equation and the precision of prediction making.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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