The joys and perils of working on stream and riverine fishes is that the causes for changes in fish assemblages or populations is seldom obvious at first glance. Take a look at this paper which summarizes a very large investigation of declines in fish in Swiss Rivers.
The photo here is of the the Lütschine River
It is a fast- flowing glacier fed river that is popular among tourists who must raft it. Not all Swiss rivers look this way but it is the way we think about foreign lands from travel brochures.
Now click on the link and see what seems to explain "where have all the fish gone" in Swiss Rivers. I was surprised. You may be also.
Post your precis here for articles you read about Ecosystems Issues for Wednesday's discussion.
Have a nice weekend
4 comments:
Up to 10 blockages per 1 km of stream, that is incredible! Is that number correct!
In their journal paper ‘Where Have All the Fish Gone: The reasons why fish catches in Swiss Rivers are Declining’, Burkhardt-Holm et al (2005) propose a multi-factor cause to the vanishing stocks of fish in Swiss streams and rivers. They support this assertion by employing two approaches: development of a Bayesian probability network to summarize the qualitative and quantitative information to study the manifold interrelations among the various factors; and the weight-of-evidence analysis approach, which aims at evaluating the available evidence as objectively as possible. Before the authors propose remediation strategies, they advice that any proposed measure must clearly be adapted to local conditions, because of space limitations. Burkhardt-Holm et al (2005) aim to demonstrate the extent to which anthropogenic factors impact on stream and river fish stocks.
Burkhardt-Holm P., H. Güttinger, U. Ochsenbein, A. Peter, K. Scheurer, H. Segner, E. Staub, M. J.-F. Suter (2005). Where Have All the Fish Gone: The reasons why fish catches in Swiss Rivers are Declining, Environmental Science & Technology 441–447.
James et al. (2007), in their journal paper ‘Land use controls nutrient excretion by stream invertebrates along a gradient of agriculture’, assert that agricultural land use in the watersheds of streams affects mass-specific excretion rates of N and P by mayflies. They support this assertion by measuring mayfly excretion rates and molar ratios of dissolved organic C (DOC), NH4, and soluble reactive P (SRP) in six streams flowing through watersheds with contrasting agricultural land use. The authors accept the fact that they do not know whether ambient environmental factors, such as temperature, or other metabolic predictors such as body mass or larval instar can explain the variable release ratios observed in their study. The main purpose of James et al is to add to the dearth of knowledge on the relationships between nutrient ratios in food and consumer release ratios in streams flowing through heterogeneous landscapes.
James L. A. H., M. A. Xenopoulos, H. F. Wilson and P. C. Frost(2007). Land use Controls Nutrient Excretion by Stream Invertebrates along a Gradient of Agriculture, J. N. Am. Benthol. Soc., 26(3):523–531.
In their journal article, “Effects of stream restoration on denitrification in an urbanizing watershed,” Kaushal et al. (2008) assert that geomorphic stream restoration, often preformed with water quality issues in mind, may enhance the ability of streams to convert nitrate to nitrogen gas. Using a stable isotope method known as a “push-pull” the authors found that rates of denitrification were significantly greater in a restored stream reach than an unrestored reach in an urbanized Maryland stream. The authors admit some uncertainty with the push-pull method, that the addition of nitrate to the system might artificially increase denitrification because of stimulated microbial activity and additionally the intensive nature of this method limited the sample size of the study to two reaches. The purpose of this paper was to quantitatively consider a water quality benefit to stream restoration and stimulate considering water quality aspects to future restoration projects.
Kaushal, S.S., P.M. Groffman, P.M. Mayer, E. Striz, and A.J. Gold. 2008. Effects of stream restoration on denitrification in an urbanizing watershed. Ecological Applications 18:789-804.
Post a Comment