Chapter 5 Water table elevation controls on soil nitrogen cycling in riparian wetlands along a ...

200 Pages·2003·10.76 MB·English

Nitrogen transformation and
retention in riparian buffer zones
Stikstofomzettingen en -retentie in
beekbegeleidende bufferzones
(met een samenvatting in het Nederlands)
Proefschrift
Ter verkrijgen van de graad van doctor
aan de Universiteit Utrecht
op gezag van de Rector Magnificus,Prof.Dr.W.H.Gispen,
ingevolge het besluit van het College van Promoties
in het openbaar te verdedigen
op maandag 24 november 2003
des ochtends te 10.30 uur
door
Maria Margaretha Hefting
Geboren op 08 december 1967 te Ede
Promotores Prof.Dr.J.T.A.Verhoeven
Prof.Dr.D.F.Whigham
Faculty of Biology,Landscape Ecology group
Utrecht University
Co-promotor Dr.G.Pinay
Centre d’Ecologie Fonctionnelle & Evolutive
CNRS Montpellier
France
ISBN 90-393-3554-0
Cover photo Michiel van Dongen
Cover design Barbara Bovenschen
Lay-out Marjolein Kortbeek-Smithuis
Printing Febodruk BV (Enschede,Utrecht)
N
NICOLAS
The results reported in this thesis were collected as part of
a European project on nitrate buffer zones,the NICOLAS project
(NItrogen COntrol by LAndscape Structures in agricultural environments).
This project was funded by the European commission DG XII
(Scientific Advisor,H.Barth),grant number ENV4-CT97-0395.

Contents
1 General introduction 7
2 Water quality dynamics and hydrology in riparian zones 25
in the Netherlands
3 Nitrous oxide emission and denitrification in chronically 49
nitrate-loaded riparian buffer zones
Journal of Environmental Quality 32:1194-1203(2003)
4 Spatial variation in denitrification and N O emission 67
2
in relation to nitrate removal efficiency in an N stressed
riparian buffer zone
5 Water table elevation controls on soil nitrogen cycling 89
in riparian wetlands along a European climatic gradient
Biogeochemistry,67(1), in press (2004)
6 The role of vegetation and litter in the nitrogen dynamics 107
of riparian buffer zones in Europe
Ecological Engineering, accepted (2004)
7 Nitrogen transformation and retention in riparian buffer zones: 133
a synthesis
References 153
Summary 175
Nederlandse samenvatting 183
Dankwoord 191
CV 197

Chapter 1
General introduction
with Jos Verhoeven
Introduction
In many parts of the western world,the drastic changes in agricultural practice
in the 20th century have fundamentally changed the way in which landscapes
function.Not only have many agricultural fields been drained and have stream
beds been straightened and hardened,also the use of ever increasing amounts
of inorganic fertilizer has augmented and altered patterns of nutrient flux
between agricultural fields and the surrounding countryside. In the
Netherlands,nutrients were historically transferred from large heathland areas
and wet grasslands towards the crop fields,nowadays fertilizer applications are
so high that considerable amounts of nutrients leach from the upland fields
into the groundwater and further towards lower areas and aquatic systems,
where they cause severe eutrophication.These problems need to be solved,
and there is considerable interest in ways to strengthen natural capacities of
landscape structures to retain or even remove nutrients.This thesis investigates
the functioning of riparian buffer zones as habitats for nutrient removal.One
of the study areas was North East Twente (the Netherlands),an area illustrative
for the agricultural development,where the use of riparian buffer zones could
make a difference in nutrient transport to streams.
Figure 1 Sheep grazing in the Hazelbekke valley (Bernink, 1926).
Nutrient fluxes in Dutch agricultural landscapes;
from converging to diverging flows
The Pleistocene sand area in the eastern part of the Netherlands, has been
used by man since prehistoric times.The first agricultural activities started in
the early Middle Ages,and from about 1200 rye was grown on communal crop
fields (“essen”) situated on the best drained parts of the landscape,mostly the
higher flanks of glacial moraines and on sand dunes. Farmers kept herds of
sheep, which grazed the surrounding heathlands and wet grasslands (Fig. 1,
from Bernink,1926).Overnight sheep were kept in stables (“potstal”) on sods
of heather,which were regularly cut from the heathland areas.To make the
poor sandy soils more fertile, sods with sheep excrements were put on the
communal crop fields. On these fields organic matter and nutrients
accumulated over centuries,creating fertile soils (“eerdgronden”) with layers
rich in organic matter eventually reaching a thickness of about 1 metre.The
heathlands on the other hand became nutrient poor,developing acid podzolic
soils and eventually became overexploited,which led to bare sand “deserts”.
With the introduction of chemical fertilizers in the beginning of the last
century,patterns of nutrient flows in the landscape changed dramatically.The
fertility of the crop fields became independent of the surrounding land and
the use of fertilizers made it possible to use the nutrient-poor heathlands and
moist grasslands for agricultural production.Reallotment schemes subsidized
8 • Chapter 1
by the Dutch government resulted in larger agricultural fields and better
drainage. Consequently, most of the riparian buffer zones and hedgerows,
landscape elements considered to be of little importance, disappeared.
Nowadays,however,both are highly valued from the perspective of biodiversity
and for their role as nutrient sink,maintaining water quality.Fertilizer levels
increased,following the rapid intensification of agriculture,until the late 1980’s
to application rates of over 350 kg N ha-1. The use of large amounts of
inorganic fertilizer and import of high-energy fodder in agricultural practice
resulted in considerable nutrient surpluses and consequently to considerable
nutrient losses to the ground- and surface waters.
Diffuse nitrogen pollution
Today,agricultural activities are considered the main source of nutrient inputs,
such as nitrogen (N) and phosphorus (P),to terrestrial and aquatic ecosystems.
Leaching of nutrients leads to degraded water quality with negative potential
impacts on human health and the environment.The contamination of surface
water and groundwater with nitrogen is particularly severe in European
agricultural environments (Meybeck and Helmer,1989;Isermann,1990).In
the Netherlands,70% of the nitrogen pollution originate from agriculture (Van
Eerdt and Fong, 1998).The loss of nitrogen compounds from agricultural
environments to the shallow groundwater and surface water has increased
dramatically over the last decades (Oenema et al.,1998;Van Eerdt and Fong,
1998).Although several agricultural measures are being used to reduce the
amount of excessive nitrogen in the soil profile after harvest,leaching of nitrate
still takes place, polluting the shallow groundwater (Addiscot et al., 1991;
Olsthoorn and Fong,1998;Ondersteijn et al.,2002).
Possible health hazards of high nitrogen concentrations in drinking water are
‘the blue baby syndrome’and stomach cancer (Harrisson,1996).Although the
probability of these hazards is very low due to thorough drinking water
purification, the costs of water purification are high and will continue to
increase in the future if nutrient pollution by agriculture continues.Diffuse
nitrogen pollution of shallow groundwater remains of major concern since it
causes eutrophication of fresh surface waters and marine waters affecting the
functioning and biodiversity of aquatic ecosystems. Consequently, the
reduction of diffuse nitrate pollution from intensive agriculture is one of the
main issues in the EU Water Framework Directive.The Nitrate Directive
(1991) prescribes an maximum concentration of 50 mg nitrate l-1 in
groundwater, which is equivalent to 11.3 mg N l-1. However in many
agricultural areas in Europe this threshold is exceeded, especially in the
Introduction • 9
Netherlands, which has the most intensive agriculture in terms of external
nutrient inputs (Van Bruchem et al.,1999;Ondersteijn et al.,2002).Because
source-directed measures such as the Mineral Accounting System (MINAS),
are not immediately reflected in changes in nutrient loads to the surface water,
additional measures to directly reduce surface water enrichment should be
implemented (Oenema et al.,1998;De Wit and Behrendt,1999).
Riparian buffers are examples of habitats that can be used directly to decrease
nutrient loading of surface waters. This thesis specifically deals with the
nitrogen transformation processes in riparian buffer zones and their potential
to improve water quality within different climatic zones and in areas with high
nitrogen loading.
What are buffer zones?
Buffer zones are landscape elements,located at the interface between terrestrial
and aquatic ecosystems,which can intercept nutrients from shallow subsurface
runoff before it reaches the surface water.Buffer zones may differ in size and
layout;hence several definitions and terms are used in the literature to indicate
buffer zones, ranging from narrow fertilizer-free strips to large (natural)
riverine wetlands. The wide range of possible landscape structures with
potential for nutrient retention is indicated in Figure 2.In this study we focus
on the buffer function of (semi) natural riparian zones (3a/d,Fig.2) of 10-30
m width along lower-order streams (1st - 4th order).In this thesis we use the
terms riparian buffer zone,riparian zone and buffer zone as synonyms.The
term strip is used to distinguish specific parallel areas within the riparian buffer
zone.
Processes of nitrogen transformation in riparian
buffer zones
Riparian zones are important components of stream ecosystems as they are
intimately linked to the functioning of the stream channel by influencing
stream bank stability,water temperature,primary production and biodiversity
(Hynes, 1983; Naiman and Décamps, 1997). Due to their position between
upland and aquatic systems,riparian zones contribute to the control of energy,
nutrients and organic matter fluxes both in longitudinal (Schlosser and Karr
1981;Pinay et al.,2000) and lateral directions (Peterjohn and Correll 1984;
Haycock et al.,1997).In this perspective natural riparian zones can function
10 • Chapter 1