C.A.J. Appelo

Bio: C.A.J. Appelo is an academic researcher from VU University Amsterdam. The author has contributed to research in topics: Groundwater & Water well. The author has an hindex of 4, co-authored 8 publications receiving 4991 citations.

Geochemistry, groundwater and pollution

Abstract: Groundwater geochemistry is an interdisciplinary science concerned with the chemistry in the subsurface environment. The chemical composition of groundwater is the combined result of the quality of water that enters the groundwater reservoir and reactions with minerals and organic matter of the aquifer matrix may modify the water quality. Apart from natural processes as controlling factors on the groundwater quality, in recent years the effect of pollution, such as nitrate from fertilizers and acid rain, also influences the groundwater chemistry. Due to the long residence time of groundwater in the invisible subsurface environment, the effect of pollution may first become apparent tens to hundreds of years afterwards. A proper understanding of the processes occurring in aquifers is required in order to predict what the effect of present day human activities will be on that scale. This book presents a comprehensive and quantitative approach to the study of groundwater quality. Practical examples of application are presented throughout the text.

Introduction to Groundwater Geochemistry

Abstract: Groundwater geochemistry is the science that explores the processes controlling the chemical composition of groundwater, the groundwater quality. The groundwater quality influences the use of this resource. Groundwater may contain hazardous substances that affect health when consumed or which deteriorate the environment when the water is thoughtlessly spilled at the surface. The groundwater quality may change during the exploitation or it may be affected by human activities of which the impact is not always immediately evident. The interest of society in groundwater geochemistry is mainly to ensure good quality drinking water. Although drinking water can be manufactured, for example by desalinization, this still is a costly affair, and to surrender to this option is in conflict with our desire to utilize groundwater as a sustainable resource, refreshingly and cleanly flowing from a well. Preservation of good groundwater therefore has a high priority for environmental authorities. This chapter introduces basic subjects such as the concentration units, water sampling techniques, and how to examine the accuracy of a chemical analysis. We begin with the concentration limits for drinking water.

Denitrification across landscapes and waterscapes: a synthesis.

Abstract: Denitrification is a critical process regulating the removal of bioavailable nitrogen (N) from natural and human-altered systems. While it has been extensively studied in terrestrial, freshwater, and marine systems, there has been limited communication among denitrification scientists working in these individual systems. Here, we compare rates of denitrification and controlling factors across a range of ecosystem types. We suggest that terrestrial, freshwater, and marine systems in which denitrification occurs can be organized along a continuum ranging from (1) those in which nitrification and denitrification are tightly coupled in space and time to (2) those in which nitrate production and denitrification are relatively decoupled. In aquatic ecosystems, N inputs influence denitrification rates whereas hydrology and geomorphology influence the proportion of N inputs that are denitrified. Relationships between denitrification and water residence time and N load are remarkably similar across lakes, river reaches, estuaries, and continental shelves. Spatially distributed global models of denitrification suggest that continental shelf sediments account for the largest portion (44%) of total global denitrification, followed by terrestrial soils (22%) and oceanic oxygen minimum zones (OMZs; 14%). Freshwater systems (groundwater, lakes, rivers) account for about 20% and estuaries 1% of total global denitrification. Denitrification of land-based N sources is distributed somewhat differently. Within watersheds, the amount of land-based N denitrified is generally highest in terrestrial soils, with progressively smaller amounts denitrified in groundwater, rivers, lakes and reservoirs, and estuaries. A number of regional exceptions to this general trend of decreasing denitrification in a downstream direction exist, including significant denitrification in continental shelves of N from terrestrial sources. Though terrestrial soils and groundwater are responsible for much denitrification at the watershed scale, per-area denitrification rates in soils and groundwater (kg Nkm � 2 � yr � 1 ) are, on average, approximately one-tenth the per-area rates of denitrification in lakes, rivers, estuaries, continental shelves, or OMZs. A number of potential approaches to increase denitrification on the landscape, and thus decrease N export to sensitive coastal systems exist. However, these have not generally been widely tested for their effectiveness at scales required to significantly reduce N export at the whole watershed scale.