Global Change Abstracts The Swiss Contribution - SCNAT

Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems
08.1-258
Implementation of a process-based catchment
model in a poorly gauged, highly glacierized
Himalayan headwater
Konz M, Uhlenbrook S, Braun L, Shrestha A, Demuth
S
Switzerland, Netherlands, Germany, Nepal
Modelling , Hydrology
The paper presents a catchment modeling approach
for remote glacierized Himalayan catchments.
The distributed catchment model TAC
(D), which is widely based on the HBV model, was
further developed for the application in highly
glacierized catchments on a daily timestep and
applied to the Nepalese Himalayan headwater
Langtang Khola (360 km(2)). Low laying reference
stations are taken for temperature extrapolation
applying a second order polynomial function.
Probability based statistical methods enable
bridging data gaps in daily precipitation
time series and the redistribution of cumulated
precipitation sums over the previous days. Snow
and ice melt was calculated in a distributed way
based on the temperature- index method employing
calculated daily potential sunshine durations.
Different melting conditions of snow and ice and
melting of ice under debris layers were considered.
The spatial delineation of hydrological response
units was achieved by taking topographic
and physiographic information from maps and
satellite images into account, and enabled to
incorporate process knowledge into the model.
Simulation results demonstrated that the model
is able to simulate daily discharge for a period of
10 years and point glacier mass balances observed
in the research area with an adequate reliability.
The simple but robust data pre-processing and
modeling approach enables the determination of
the components of the water balance of a remote,
data scarce catchment with a minimum of input
data.
Hydrology and Earth System Sciences, 2007, V11,
N4, pp 1323-1339.
08.1-259
Effects of impoundment on nutrient availability
and productivity in lakes
Matzinger A, Pieters R, Ashley K I, Lawrence G A,
Wüest A
Switzerland, Canada
Modelling , Limnology , Marine & Freshwater Biology
, Geochemistry & Geophysics
We investigate the hydraulic alteration and the
effect on primary productivity of the Hugh Keenleyside
Dam built at the outlet of the Arrow Lakes
(British Columbia, Canada) in 1967. Three dam-
135
induced hydraulic changes have been identified
as relevant: (1) water level increase, (2) leveling of
the seasonal outflow, and (3) subsurface release of
water from the dam. The potential effect of these
alterations on primary productivity were tested
with a numerical model supported by field observations.
Hydraulic modifications can reduce lake
productivity by up to 40%, primarily as a result
of altered flow path and allowing nutrients to
pass through the reservoir without entering the
productive zone near the surface. This productivity
loss is comparable to the reduction caused
by nutrient retention behind dams constructed
upstream of the Arrow Lakes Reservoir. The combined
productivity loss from both of these two
mechanisms is significant and may well be responsible
for the dramatic decline of kokanee (Oncorhynchus
nerka) observed in the Arrow Lakes
Reservoir in the 1990s.
Limnology and Oceanography, 2007, V52, N6,
NOV, pp 2629-2640.
08.1-260
Eutrophication: are mayflies (Ephemeroptera)
good bioindicators for ponds?
Menetrey N, Oertli B, Sartori M, Wagner A, Lachavanne
J B
Switzerland
Zoology , Marine & Freshwater Biology , Water
Resources , Biodiversity
Ephemeroptera larvae are recognized worldwide
for their sensitivity to oxygen depletion in running
waters, and are therefore commonly used as
bioindicators in many monitoring programmes.
Mayflies inhabiting lentic waters, like lakes and
ponds, in contrary have been poorly prospected
in biomonitoring. For this purpose, a better understanding
of their distribution in lentic habitats
and of the relations of species presence with
environmental conditions are needed. Within
this framework, 104 ponds were sampled in Switzerland.
The Ephemeroptera are found to be an
insect order particularly well represented in the
ponds studied here (93% of the lowland ponds).
Nevertheless, in terms of diversity, they are relatively
poorly represented (mean species number
= 1.9). Two species dominated: Cloeon dipterum
(Baetidae) and Caenis horaria (Caenidae). The investigations
contributed to the updating of the
geographical distribution of the species in Switzerland,
as many of the observations appear to
be from new localities. The trophic state of ponds
appears here to be important for Ephemeroptera
communities. First, there is a negative relationship
between total phosphorus (TP) concentrations
and species richness. Second, the presence of