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Headwater influences on downstream water quality.

ABSTRACT: We investigated the influence of riparian and whole watershed land use as a function of stream size on surface water chemistry and assessed regional variation in these relationships. Sixty-eight watersheds in four level III U.S. EPA ecoregions in eastern Kansas were selected as study sites. Riparian land cover and watershed land use were quantified for the entire watershed, and by Strahler order. Multiple regression analyses using riparian land cover classifications as independent variables explained among-site variation in water chemistry parameters, particularly total nitrogen (41%), nitrate (61%), and total phosphorus (63%) concentrations. Whole watershed land use explained slightly less variance, but riparian and whole watershed land use were so tightly correlated that it was difficult to separate their effects. Water chemistry parameters sampled in downstream reaches were most closely correlated with riparian land cover adjacent to the smallest (first-order) streams of watersheds or land use in the entire watershed, with riparian zones immediately upstream of sampling sites offering less explanatory power as stream size increased. Interestingly, headwater effects were evident even at times when these small streams were unlikely to be flowing. Relationships were similar among ecoregions, indicating that land use characteristics were most responsible for water quality variation among watersheds. These findings suggest that nonpoint pollution control strategies should consider the influence of small upland streams and protection of downstream riparian zones alone is not sufficient to protect water quality.

SUBMITTER: Dodds WK

PROVIDER: S-EPMC2242854 | biostudies-other | 2008 Mar

REPOSITORIES: biostudies-other

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Project description:BackgroundIn order to regulate water flow, hydraulic structures such as weirs or checks, frequently equipped with gates, are used. Water can flow below or over the gate or, simultaneously, over and below the gate. Both diversifications of hydraulic gradient, being an effect of damming up a river by the structure and shear stresses at the bed, which exceeds the critical shear stress value, invoke the local scouring downstream the structure. This phenomenon has been studied in laboratory and field conditions for many years, however Researchers do not agree on the parameters that affect the size of the local scour and the intensity of its formation. There are no universal methods for estimating its magnitude However, solutions are sought in the form of calculation formulas typical for the method of flow through the structure, taking into account the parameters that characterize a given structure. These formulas are based on factors that affect the size of the local scours, that is, their dimensions and location. Examples of such formulas are those contained in this article: Franke (1960), Straube (1963), Tarajmovič (1966), Rossinski & Kuzmin (1969) equations. The need to study this phenomenon results from the prevalence of hydrotechnical structures equipped with gates (from small gated checks to large weirs) and from potential damage that may be associated with excessive development of local erosion downstream, including washing of foundations and, consequently, loss of stability of the structure.MethodsThis study verifies empirical formulas applied to estimate the geometry parameters of a scour hole on a laboratory model of a structure where water is conducted downstream the gate with bottom reinforcements of various roughness. A specially designed remote-controlled measuring device, equipped with laser scanner, was applied to determine the shape of the sandy bottom. Then the formula optimization is conducted, using Monte Carlo sampling method, followed by verification of field conditions.ResultsThe suitability of a specially designed device, equipped with laser scanner for measuring the bottom shape in laboratory conditions was demonstrated. Simple formula describing local scour geometry in laboratory conditions was derived basing on the Straube formula. The optimized formula was verified in field conditions giving very good comparative results. Therefore, it can be applied in engineering and designing practices.

Project description:Introduction: Repeated administration of abused drugs, including ?9-tetrahydrocannabinol (THC), induces the stable transcription factor ?FosB in dopaminergic terminal field regions of the mesolimbic system. These studies investigated the effect of prior repeated THC treatment on THC-induced ?FosB expression and regulation of downstream targets in the forebrain. Methods: Mice received THC (10?mg/kg) or vehicle twice daily for 13 days, and then half of each group received a single injection of THC or vehicle 45?min before brain collection. ?FosB messenger RNA (mRNA) and protein were measured by polymerase chain reaction and immunoblotting, respectively. Potential downstream targets of ?FosB induction were measured by immunoblot. Results: THC injection in mice with a history of repeated THC treatment enhanced ?FosB expression as compared with vehicle in the prefrontal cortex (PFC), nucleus accumbens (NAc), and amygdala. This change occurred concomitantly with an increase in ?FosB mRNA in the PFC and NAc. THC injection in mice with a history of repeated THC treatment increased expression of cyclin-dependent kinase 5 (Cdk5) and its regulatory protein p35 only in the PFC. This increase in Cdk5 and p35 expression in PFC was also found in mice that had only received repeated THC administration, suggesting that this effect might be due to induction of ?FosB. Extracellular signal-regulated kinase (ERK) phosphorylation was increased in PFC after THC injection in repeated THC-treated mice. Phosphorylation of glycogen synthase kinase-3? (GSK3?), a Cdk5 target, was reduced in PFC after repeated THC treatment regardless of THC history, and phosphorylation of dopamine- and cAMP-regulated phosphoprotein of 32?kDa (DARPP-32) at the Cdk5-regulated threonine 75 site was unchanged. Conclusion: These results suggest that a history of repeated THC administration primes THC-mediated induction of ?FosB in the NAc and PFC, and that expression of both downstream targets of ?FosB (e.g., Cdk5 and p35) and upstream activators (e.g., pERK) in the PFC is dependent on THC history, which might have functional implications in addiction and neuropsychiatric disease.

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Headwater influences on downstream water quality.

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