Slow Recovery of Headwater-Stream Fishes Following a Catastrophic Poisoning Event

Accidental spills of chemicals and other pollutants can decimate populations of stream-dwelling species. Recovery from such accidents can be relatively fast and complete when the affected stream reaches can be recolonized from upstream and downstream sources. However, faunal recoveries from accidental spills that extirpate populations from entire headwater streams have not been extensively documented, and understanding resilience of headwater-stream biota is relevant for assessing threats to at-risk species. We assessed recovery of fish populations in a 5.7-km-long headwater stream in the southeastern United States following a complete, or nearly complete, fish-kill caused by a chemical spill near the source of the stream. We sampled for fishes at five stream locations, two downstream and three upstream from a perched, culverted road-crossing located 2.4 km upstream from the stream mouth, over a period of 18.5 mo following the poisoning event. We observed 11 fish species, representing ≤65% of the fish species expected based on occurrences in nearby tributary streams. In postpoisoning sampling, only three of these taxa were observed upstream of the culvert; all 11 species, including the federally threatened Cherokee Darter Etheostoma scotti, were found downstream of the culvert but were mostly represented by a few, large individuals. In contrast, dead individuals of at least eight taxa including the Cherokee Darter were observed upstream of the culvert at the time of the fish-kill. These observations provide evidence of slow recovery of a headwater fish fauna, and especially upstream of a barrier to fish movement, where the recolonization sources are primarily downstream. Additional case studies may reveal whether this result applies generally to headwater streams. Slow recovery could make species that primarily inhabit or maintain greatest abundances in headwaters, including multiple at-risk fishes, particularly vulnerable to the threat of accidental spills that result in local population extirpation.

Small hydraulic structures, big environmental problems: is it possible to mitigate the negative impacts of culverts on stream biota?

The present study is a broad and critical review of the transdisciplinary literature on the construction of culverts and their impacts on stream hydrology and geomorphology as well as on stream habitats and biota. For engineers, a culvert is a structure, usually of the tunnel type, that transfers a stream or open drain under a road, railway line or other obstacle from one side to the other. In fact, culverts are complex hydraulic structures whose impacts on stream ecosystems must be evaluated and understood before they are designed. The objective of this paper is to analyse and discuss recent knowledge about culvert functioning in terms of their negative effects on the passage of freshwater biota, particularly fish, and on entire stream ecosystems. We present the results of many studies showing that improperly designed culverts are barriers for migrating animals and usually have serious ecological consequences (mainly fish life history disturbances). We also pay attention to different culvert modification methods that increase their passability for organisms and mitigate culvert impacts on the surrounding environment. The other purpose of this review is therefore to emphasize that the integration of the knowledge and professional experience of biologists and ecologists with those of river managers, river engineers, hydraulic engineers, hydrologists and geomorphologists is necessary to design culverts that preserve the natural properties of streams.

Heavily burned wood from wildfires is less likely to provide substrate for stream biota

Increasingly severe forest fires are recruiting more heavily burned wood into streams. Wood affects every ecological and physical process in streams differently throughout seasons. However, little is known about the seasonality of wood functions in fire-prone biomes and how it combines with wood burning level to guide future postfire restoration efforts.Through an extensive three-year seasonal tracking of stream wood following forest fires in central Portugal, we examined for the first time the influence of burning level, season, and a large suite of driving factors on the likelihood of each of four functions with primary ecological consequences — retention of organic matter, serving as substrate for aquatic biota, being key pieces forming wood jams, and deflecting flow including pool habitat formation.Our results strongly support that one of the main ecological functions of wood in rivers, i.e. to provide substrate for biological organisms — namely for vegetation, periphyton, biofilms, and ovipositions — can be negatively affected in heavily burned wood.Except for jam formation, the probability of each stream wood function changed markedly with season and the probability of non-function was nearly twice as high in the Euro-Mediterranean dry as in the wet season.More anchored and decayed wood increased the probability of all functions, whereas the effect of submergence depended on the function. Challenging the “size paradigm” assuming larger-sized pieces to provide more function, our data suggest the effect of size to be function-specific.Synthesis and applications. We show how postfire restoration success can be maximized by selecting the most appropriate wood, taking advantage of attribute-function relationships and choosing the right timing for operations. We urge managers to refrain from removing wood or to selectively remove the most heavily carbonized only, allowing the persistence of great potential to provide substrate for stream biota. The non-attraction of heavily burned wood as substrate can be compensated for by other wood with attributes enhancing this function, such as wood deeper within the bankfull area, and with large diameters. These results help to inform successful management, as is increasingly asked from restoration ecology.

Advances in Understanding Landscape Influences on Freshwater Habitats and Biological Assemblages

<i>Abstract.</i>—Surrounding land use and cover can have profound effects on the physical, chemical, and biological properties of stream ecosystems. For this reason, changes in land use and cover throughout catchments often have strong effects on stream ecosystems that are particularly interesting to researchers. Additionally, natural physical and climatic, or physiographic, characteristics are important for determining natural land cover and constraining human land use and are also strongly related to stream habitat and biota. Because the physiographic template differs among catchments and is an important mediator of catchment processes, it is important to account for natural physiographic differences among catchments to understand the relationship between land use/cover and stream biota. In this paper, we develop and assess the usefulness of a regional framework, land use/cover distinguished physiographic regions (LDPRs), which is designed for understanding relationships between land use/cover and stream biota while accounting for the physiographic template. We classified hydrologic units into LDPRs based on physiographic predictors of land use and cover for the eastern and western United States through the use of multivariate regression tree analysis. Next, we used case study data to assess the usefulness of LDPRs by determining if the relationships between fish assemblage function and land use/cover varied among classes using hierarchical logistic regression models. Eight physiographic characteristics determined land cover patterns for both the eastern and western United States and were used to classify hydrologic units into LDPR classes. Five commonly used biotic metrics describing trophic, reproductive, and taxonomic groupings of fish species responded in varying ways to agriculture and urban land use across LDPRs in the upper Mississippi River basin. Our findings suggest that physiographic differences among hydrologic units result in different pathways by which land use and cover affects stream fish assemblages and that LDPRs are useful for stratifying hydrologic units to investigate those different processes. Unlike other commonly used regional frameworks, the rationale and methods used to develop LDPRs properly account for the often-confounded relationship between physiography and land use/cover when relating land cover to stream biota. Therefore, we recommend the use and refinement of LDPRs or similarly developed regional frameworks so that the varying processes by which human land use results in stream degradation can be better understood.