Freiburger Schriften zur Hydrologie
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Band/volume 18: EISELE M. (2003):
Stoffhaushalt und Stoffdynamik in Flusseinzugsgebieten:
Ein Beitrag zum Bewertungsverfahren "Hydrologische Güte"
To overcome the lack of catchment oriented assessment procedures in the
field of water protection an assessment procedure for the hydrological
quality of meso-scale catchments was developed at the Institute of Hydrology,
University of Freiburg. The main aim of the project was the development
and presentation of an adequate methodology and its application in a set
of test catchments. The procedure is divided into the assessment units
catchment properties, runoff dynamics and nutrient budgets, water quality
and solute dynamics. In this study theoretical backround, development
and application of the assessment unit nutrient budget, water quality
and solute dynamics are presented.
First an overview on the actual research status concerning water quality
and on existing methodologies for the description and assessment of nutrient
transport and water quality is given. The methodology of the assessment
procedure was developed in selected test catchments and subsequently applied
in different river basins in South-West Germany which cover a large variety
of scale, natural properties, land use structures and water resources
issues. To establish a basis for the application of the procedure a GIS-based
catchment analysis was carried out for the investigated river basins.
A short description of the assessment of catchment properties and runoff
dynamics is given in addition to demonstrate the concept of the entire
In the framework of the development experimental investigations in sub-catchments
of the Dreisam river basin and a study of the capability of a water quality
model was carried out. The results of the experimental investigations
demonstrate a different temporal behaviour of solutes due to their chemical
properties and dominating transport paths. In the modelling study the
limits of complex conceptual models in larger areas are revealed.
The methodology of the assessment unit nutrient budget, water quality
and solute dynamics is based on established conceptual approaches and
uses only readily available input data. In the approach the nutrients
nitrogen and phosphorus which are crucial for the problem of eutrophication
In the parameter group nutrient budget an assessment of nutrient emissions
into surface water and groundwater on the basis of a spatially distributed
water and nutrient balance is carried out. The nutrient input is derived
from the nutrient surplus which is calculated for all permeable land surfaces
based on the land use classification and agricultural statistics using
calculation methods and values described in literature.
In the distributed water balance interpolated data of mean annual precipitation
and the results of a simulation of the actual evapotranspiration are used.
The resulting spatially distributed mean annual discharge is further divided
into the runoff components fast runoff, delayed runoff,
and base flow. The component fast runoff is an
estimation of surface runoff, macropore flow and drainage runoff. It is
quantified by using empirical functions and spatially distributed data
of topography, soil characteristics and land use. Quantification of the
base flow component is derived using results from base flow separations
in sample catchments which were regionalized for all the investigated
river basins. Delayed runoff is quantified from the residue of the two
other components. The mobilization of nutrients is estimated using the
described runoff components, soil characteristics (field capacity) and
a coefficient describing the chemical behaviour. To quantify the transport
of sediment associated phosphorus a simplified sediment delivery calculation
is executed based on data of topography and land use. Nutrient losses
in the vadose zone and groundwater aquifer are estimated based on measured
values of groundwater concentrations. The nutrient delivery from point
sources is quantified based on statistical data for sewage plants and
canalisation as well as data for precipitation and the area of impermeable
land surfaces. Nutrient retention and denitrification in the river system
is quantified empirically based on the hydraulic impact. To achieve a
validation of the nutrient balance the resulting concentrations in surface
water are compared to long term means of measured concentrations.
The nutrient budget is assessed referring to the potential natural
status for which a natural vegetation and the absence of direct
human impacts is assumed. For the simulation of the potential natural
status of nutrient emissions all land use classes are parameterized
using the nutrient input and water balance terms for forest vegetation.
Finally the nitrogen and phosphorus budgets are assessed by comparing
the actual and potential natural status. In an uncertainty analysis the
range of potential simulation errors in water and nutrient balance is
estimated. The resulting uncertainty range in the assessment can be estimated
to a maximum error of one quality class.
In the parameter group water quality and solute dynamics the status of
water quality in the surface waters is assessed. The water quality in
the river system is quantified based on measured or simulated concentrations
of nitrogen and phosphorus and assessed using chemical water quality standards.
For catchments with long term measurements the temporal variability is
taken into account by an assessment of solute dynamics. For this purpose
monthly nutrient loads are calculated and assessed using monthly reference
loads. The reference loads are derived from combining monthly values of
stream flow with the concentrations levels given in the water quality
standard. By the use of stream flow related loads a direct comparison
with the nutrient emissions calculated in the nutrient balance is enabled.
From the water and nutrient balance emissions of nitrogen and phosphorus
for the actual and the potential natural status are derived in each river
basin. The results are classified into quality classes. The calculated
nutrient loads are mainly a reflection of land use structures in the catchment,
nutrient surplus on the farm lands and the number and size of sewage systems.
In the validation of the resulting simulated concentrations in surface
waters using the means of long term measurements a satisfying agreement
was achieved (Nitrogen: mean relative deviance:-6 %; r² = 0,94; Soluble
phosphorus: mean relative deviance: 14 %; r² = 0,88). In the parameter
group nutrient budget the quality class is mainly determined by land use
and nutrient input in the catchment. The parameter group water quality
and solute dynamics is also influenced by the hydrological properties
in the catchment (e.g. specific discharge, water storage capacities).
In this parameter group a reasonable estimation of the status of water
quality in surface waters which is similar to the classification using
water quality standards is produced.
In a modelling study using a complex conceptional model for the simulation
of nitrogen transport in a sub-catchment of the Dreisam basin problems
of data requirement, parameter identification and practical handling occurred.
These problems were leading to the conclusion that models of this kind
are not appropriate for operational application in the meso-scale. For
this reason a model concept for nitrogen transport which is suitable for
meso-scale applications is developed in the river basin of the Seefelder
Aach. The model is built upon an existing water balance model using its
simulation results as input variables. Due to a more simple conceptional
approach, problems of data requirement are avoided and parameter uncertainty
is reduced. As this model is used for scenario simulations of nutrient
management options an assessment of model uncertainties and the resulting
potential simulation errors is carried out.
The assessment of nutrient budget, water quality and solute dynamics is
carried out in the framework of the application of assessment procedure
hydrological quality. With the proposed methodology the basis
for an spatially orientated assessment of nutrient budgets and water quality
in meso-scale catchments is established. Apart from the quantification
of the human impact on water quality described in this study human impacts
on the water balance and the variability of stream flow are parameterized
in the two remaining assessment units catchment properties and runoff
dynamics. Therefore the methods compiled in the assessment procedure can
be helpful tools for the estimation of the significant human impacts
on the aquatic environment which has to be included in the river basin
management plans according to the new European water framework directive.
along with morphological and biological assessment procedures the assessment
of the hydrological quality will enable a holistic approach
regarding water protection, in which the catchment and its water bodies
are treated as a hydrological unit.
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