Assessing water conditions for Heleophryne rosei tadpoles and the conservation relevance

The Table Mountain Ghost Frog (Heleophryne rosei) is endemic to the Table Mountain massif and is Critically Endangered. Other than clear, clean perennial stream flow, the optimal aquatic conditions required by their larvae are unknown. Dissolved oxygen, temperature, pH, electro-conductivity, aspect and permanence of flow are the independent variables measured seasonally at two sampling altitudes at 12 rivers of the massif. Using a logistic regression model we found that a permanence of water flow and lower water temperature were significant predictors of tadpole presence. Streams with mean summer temperature above 17.2 °C, at 300 m – 400 m above sea level, do not have tadpoles. Summer and autumn abstraction should be avoided, while a summer water temperature above an average of 17.2 °C is a threshold of potential concern for management authorities responsible for biodiversity conservation, threat mitigation efforts, and bulk-water supply and abstraction.Conservation implications: The Environmental Water Reserve has not been determined for streams of Table Mountain. The requirements of the Critically Endangered Table Mountain Ghost Frog (Heleophryne rosei) can be adopted as the minimum conditions to support this species and associated communities. Perennial flow, an average January water temperature of 17.2 °C or lower.

Relationship between Peak Stage, Storm Duration, and Bank Storage along a Meandering Stream

Groundwater and surface water are often studied as different systems; however, one commonly affects the other. Bank storage, the temporary storage and release of stream water in adjacent aquifers, can contribute a considerable amount of discharge to a river and can be a component in the transport and fate of a contaminant. Studies document the effects of increasing stage and increasing storm duration; however, these controls are often investigated separately. This project examined which factor, peak stage or storm duration, was more influential on the bank-storage process. The study focused on a small reach of a third-order, meandering, perennial stream. A 3-D, transient-state numerical model (MODFLOW) was created of the study site, and 36 simulations were run at various peak stages and storm durations. Peak stage and storm durations, while both influential, affected different areas of the bank-storage process. Peak stage was statistically more influential in controlling the maximum volume of bank storage (~3.6×) and the volume of the storage that remained in the system at 100 h (~1.1×). Longer storm duration generated a slower return of water, thus increasing the retention of bank storage. Parafluvial exchange was an important factor in bank storage along a meandering stream, suggesting that at least 2-D, ideally 3-D, models need to be employed in evaluating bank storage.

Composition, abundance and biomass of a fish assemblage in a southern Brazilian coastal stream during polyhaline/euhaline condition

The coastal streams of southernmost Brazil, Rio Grande do Sul state, are marked by a period of regular marine intrusion resultant from intense oceanic winds. In the present study we aimed to investigate the species composition, abundance and relative biomass of the ichthyofauna in the lower stretch of a coastal stream during summer, a period of regular marine intrusion. Estreito is a coastal hydrological complex composed by lakes, swamps and a perennial stream, located at the central-south portion of the coastal plain of Rio Grande do Sul state. During the summer of 2018, the ichthyofauna of lower Estreito stream was sampled by beach hauls applied in 17 random points distributed in a stretch of ca. 2km. Measurements at the sampled stretch revealed salinities between 19.3 to 31.3 ppt, characterizing the studied system as polyhaline/euhaline during summer. The sample of 4,533 specimens revealed the occurrence of 20 species, being the great majority marine-dwelling. The most abundant species were the anablepid Jenynsia lineata (70.3%), the cichlid Geophagus brasiliensis (19.3%) and the the mugilid Mugil curema (7.5%). The highest relative biomass was recorded for J. lineata, followed by M. curema and G. brasiliensis. The dominance of marine-dwelling species in the assemblage composition and the high abundance of limnic-estuarine J. lineata corroborate previous studies conducted in other washouts of Rio Grande do Sul.

Missing Compensation: A Study of Compensatory Mitigation and Fish Passage in Georgia

Thousands of permit applications are filed annually with the U.S. Army Corp of Engineers, requiring significant review efforts to ensure that applications conform to regulations, and that proposed activities avoid, minimize, and compensate for stream and wetland impacts. However, the effectiveness of this approach remains uncertain. We evaluated the effectiveness of those regulatory efforts using newly installed stream–road crossings as a case study because crossings are pervasive on the landscape and many U.S. Army Corp of Engineers jurisdictions have requirements that are aimed at minimizing crossing-induced impacts to fish passage. Specifically, we assessed whether requirements intended to facilitate fish passage were implemented, whether requirements resulted in fish-passable stream–road crossings, and whether the amount of construction-related stream impact that was authorized by permits corresponded to the amount of compensation that was required. Our analysis is devoted solely to stream–road crossings in Georgia that are permitted under nationwide permits, the permit type commonly used to authorize activities in streams throughout the United States. We found that no new crossings conformed entirely to the requirements intended to avoid and minimize impacts to fish passage. The measured total stream impact length in this study was 46.0% higher than the amount of impact proposed in permit applications for perennial streams, and 23.7% higher for intermittent and ephemeral streams. Only 30.6% of the perennial stream length affected in this study received compensation for impacts even though 90.9% of impacts qualified. Collectively, these results indicate that regulations and mitigation policies are not having their intended effects of providing fish passage or preventing net loss of streams in Georgia as required under the Clean Water Act. We recommend that decision makers undertake a more geographically comprehensive evaluation of stream impacts that are authorized by permits to thoroughly evaluate regulatory effectiveness and impacts to fish passage.

Large wood recruitment and mobility in steep mountain streams of contrast European landscapes

We present a comparative study of large wood (LW) mobility in two steep channels (0.06<S<0.20) of contrast European landscapes during major hydro-geomorphic events of similar magnitude. We investigated a headwater perennial stream draining Central European medium-high mountain relief (the Klepáčský, Hrubý Jeseník Mts, Czech Republic; A≤2.5 km2) and an ephemeral Mediterranean steep stream (the Sfakiano Gorge, Crete, Greece; A≤52 km2). Both studied hydro-geomorphic events were partially accompanied by debris-flood or debris-flow character of sediment transport including significant content of LW. The minimal estimations of transported LW volume were 71.3 m3 along 1.7 km long reach in the Klepáčský and 49.4 m3 along 4 km long reach in the Sfakiano Gorge. Despite completely different characters of hydrologic regimes, riparian zones and valley confinement settings, living trees in the valley floor played crucial role in wood deposition and development of large jams in both environments. The trees living in the valley floor were the main source of LW in the studied Mediterranean channel, whereas long-term LW recruitment from very steep hillslopes or rock cliffs was quite negligible. On the other hand, previous windstorms in the Klepáčsky caused notable delivery of LW from adjacent hillslopes and LW recruitment by bank erosion occurred only at spatially-limited semi-confined parts of the valley.