Assessing and Controlling Land Use Impacts on Groundwater Quality

Abstract

Stewardship of fresh water resources is of paramount importance throughout Europe and for all environmental policies now and in the future. The problem has especially affected areas under predominantly agricultural use. The chapter provides an overview of methods used to assess soil, pore water and groundwater nutrient levels on farms and agricultural fields. We developed a zone monitoring model (ZMM) which is a basis for appropriate monitoring schemes in view of risks for the groundwater coming from agricultural lands. Based on this scheme, we describe various methods to monitor nitrate concentrations at different unit levels, from the farm to the soil zone and on to the groundwater. At farm level, nutrient balances are mandatory to identify the potentially remaining concentrations of nutrients in the soil. Nutrient balances provide an overview of nutrient levels, in particular to prevent surpluses which, as well as contaminating groundwater, could lead to environmental problems such as open water eutrophication, local air pollution and an increase in greenhouse gas emissions. Balances can be performed using operational records of nutrient application and other agronomic information (crops, yields, weather, etc.) at the farm or even field level. A catalogue of agricultural measures for groundwater conservation is available. It is to be supplemented by a methodology for the in situ monitoring of the groundwater quality as a basis for surveying the efficiency of those measures. General characteristics, the benefits and the disadvantages of recent monitoring methods are presented, summarised and rated under the heading “appropriateness for efficiency survey”. The methods described here are groundwater sampling by means of a suction lance, soil sampling beneath the groundwater table, groundwater sampling using the direct-push method, sampling from observation wells, from multi-level observation wells and from production wells. Especially in the shallow, near-surface groundwater, the concentration of dissolved substances almost instantly mirrors the effect of agriculture on the aquatic environment. It can be considered a kind of early-warning system before the surface or drinking water quality are impaired. This survey is preferably focused on nitrate, an important substance for plant nutrition known to behave as a conservative tracer carried below the root zone with the subsurface water. Computer programs have been developed for achieving the locally specific optimal strategy for groundwater-protecting land management strategies and practices. Nutrient balances are included in the latest information and communication technology (ICT) and farm management information systems (FMIS). In Germany, the methods described in this chapter are recommended as a work basis and decision tool for all bodies required to assess the efficiency of agricultural operations in the framework of legal regulations or voluntary cooperation. They can be used by farmers, landscape planners, environmentalists, water associations, water companies, decision makers and others. The whole package of decision trees and monitoring methods in the ZMM, the FMIS and ICT computer programs also has the potential to be tailored and applied to other regions.

This chapter is based largely on the guidelines from the DWA—German association for water, wastewater and waste: “Efficiency of measures to control land use for groundwater conservation—the example of nitrogen” (DWA-M 911 2013). Roland Schindler was the author responsible; Frank Eulenstein, Nils Cremer and Hartwig Drechsler were also authors of this guideline.