Determining sources of dissolved organic carbon and disinfection byproduct precursors to the McKenzie River, Oregon

This study was conducted to determine the main sources of dissolved organic carbon (DOC) and disinfection byproduct (DBP) precursors to the McKenzie River, Oregon (USA). Water samples collected from the mainstem, tributaries, and reservoir outflows were analyzed for DOC concentration and DBP formation potentials (trihalomethanes [THMFPs] and haloacetic acids [HAAFPs]). In addition, optical properties (absorbance and fluorescence) of dissolved organic matter (DOM) were measured to provide insight into DOM composition and assess whether optical properties are useful proxies for DOC and DBP precursor concentrations. Optical properties indicative of composition suggest that DOM in the McKenzie River mainstem was primarily allochthonous--derived from soils and plant material in the upstream watershed. Downstream tributaries had higher DOC concentrations than mainstem sites (1.6 +/- 0.4 vs. 0.7 +/- 0.3 mg L(-1)) but comprised < 5% ofmainstem flows and had minimal effect on overall DBP precursor loads. Water exiting two large upstream reservoirs also had higher DOC concentrations than the mainstem site upstream of the reservoirs, but optical data did not support in situ algal production as a source of the added DOC during the study. Results suggest that the first major rain event in the fall contributes DOM with high DBP precursor content. Although there was interference in the absorbance spectra in downstream tributary samples, fluorescence data were strongly correlated to DOC concentration (R2 = 0.98), THMFP (R2 = 0.98), and HAAFP (R2 = 0.96). These results highlight the value of using optical measurements for identifying the concentration and sources of DBP precursors in watersheds, which will help drinking water utilities improve source water monitoring and management programs.     

Sublethal toxicity of nano-titanium dioxide and carbon nanotubes in a sediment dwelling marine polychaete

The ecotoxicology of manufactured nanoparticles (MNPs) in estuarine environments is not well understood. Here we explore the hypothesis that nanoTiO₂ and single walled nanotubes (SWNT) cause sublethal impacts to the infaunal species Arenicola marina (lugworm) exposed through natural sediments. Using a 10 day OECD/ASTM 1990 acute toxicity test, no significant effects were seen for SWNT up to 0.03 g/kg and no uptake of SWNTs into tissues was observed. A significant decrease in casting rate (P = 0.018), increase in cellular damage (P = 0.04) and DNA damage in coelomocytes (P = 0.008) was measured for nanoTiO₂, with a preliminary LOEC of 1 g/kg. Coherent anti-stokes Raman scattering microscopy (CARS) located aggregates of TiO₂ of >200 nm within the lumen of the gut and adhered to the outer epithelium of the worms, although no visible uptake of particles into tissues was detected.     

Reconstruction of the pollution history of alkylphenols (4-tert-octylphenol, 4-nonylphenol) in the Baltic Sea

This paper reports the reconstruction of the pollution history of 4-tert-octylphenol (OP) and 4-nonylphenol (NP) in the Baltic Sea. Alkylphenols are endocrine-disrupting compound and therefore toxic to aquatic organisms. Sediment cores were collected from regions with relatively stable sedimentation conditions. The cores were dated by the ²¹⁰Pb method. The OP and NP were determined using HPLC-FL. The highest inventory of these compounds was observed in the Gotland Deep (610 μg m² of NP and 47 μg m² of OP) and the lowest—on the slope of the Gdansk Deep (24 μg m² of NP and 16 μg m² of OP). Such spatial distribution was probably, among other factors, the result of the uplift of the sea floor. The pollution trends of OP and NP in sediments coincided with the following: (1) the beginnings of eutrophication (1960s/1970s of the twentieth century) and (2) strong increase in the areal extent and volume of hypoxia and anoxia in the Baltic (present century).     

Restoring Ecological Integrity in Highly Regulated Rivers: The Role of Baseline Data and Analytical References

The goal of restoring ecological integrity in rivers is frequently accompanied by an assumption that a comparative reference reach can be identified to represent minimally impaired conditions. However, in many regulated rivers, no credible historical, morphological or process-based reference reach exists. Resilient restoration designs should instead be framed around naturalization, using multiple analytical references derived from empirically-calibrated field- and model-based techniques to develop an integrated ecological reference condition. This requires baseline data which are rarely collected despite increasing evidence for systematic deficiencies in restoration practice. We illustrate the utility of baseline data collection in restoration planning for the highly fragmented and regulated lower Merced River, California, USA. The restoration design was developed using various baseline data surveys, monitoring, and modeling within an adaptive management framework. Baseline data assisted in transforming conceptual models of ecosystem function into specific restoration challenges, defining analytical references of the expected relationships among ecological parameters required for restoration, and specifying performance criteria for post-project monitoring and evaluation. In this way the study is an example of process-based morphological restoration designed to prompt recovery of ecosystem processes and resilience. For the Merced River, we illustrate that project-specific baseline data collection is a necessary precursor in developing performance-based restoration designs and addressing scale-related uncertainties, such as whether periodic gravel augmentation will sustain bed recovery and whether piecemeal efforts will improve ecological integrity. Given the numerous impediments to full, historical, restoration in many river systems, it seems apparent that projects of naturalization are a critical step in reducing the deleterious impacts of fragmented rivers worldwide.     

Use of three bivalve species for biomonitoring a polluted estuarine environment

Estuaries are marine areas at great contamination risk due to their hydrodynamic features. PAH are wide and ubiquitous contaminants with a high presence in these marine environments. Chemical analysis of sediments can provide information, although it does not give a direct measure of the toxicological effect of such contaminants in the biota. Samples of Venerupis pullastra, Cerastoderma edule, and Mytilus galloprovincialis were collected from two locations in Corcubión estuary (Norhwest of Spain). The level of PAH in sediment and biota, and its possible origin were assessed. A moderate level of contamination was observed with a predominance of PAH of a pyrogenic origin. Genotoxic damage, measured as single-strand DNA breaks with the comet assay, was evaluated in gill tissue and in hemolymph. The values of DNA damage obtained showed a higher sensitivity of clams and cockles to the pollution load level. These differences among species make us suggest the use of some other species coupled with mussels as an optimal tool for biomonitoring estuarine environments.     

Limits to Understory Plant Restoration Following Fuel-Reduction Treatments in a Piñon–Juniper Woodland

National fuel-reduction programs aim to reduce the risk of wildland fires to human communities and to restore forest and rangeland ecosystems to resemble their historical structure, function, and diversity. There are a number of factors, such as seed bank dynamics, post-treatment climate, and herbivory, which determine whether this latter goal may be achieved. Here, we examine the short-term (2 years) vegetation response to fuel-reduction treatments (mechanical mastication, broadcast burn, and pile burn) and seeding of native grasses on understory vegetation in an upland piñon–juniper woodland in southeast Utah. We also examine how wildlife herbivory affects the success of fuel-reduction treatments. Herbaceous cover increased in response to fuel-reduction treatments in all seeded treatments, with the broadcast burn and mastication having greater increases (234 and 160 %, respectively) in herbaceous cover than the pile burn (32 %). In the absence of seeding, herbaceous cover only increased in the broadcast burn (32 %). Notably, fuel-reduction treatments, but not seeding, strongly affected herbaceous plant composition. All fuel-reduction treatments increased the relative density of invasive species, especially in the broadcast burn, which shifted the plant community composition from one dominated by perennial graminoids to one dominated by annual forbs. Herbivory by wildlife reduced understory plant cover by over 40 % and altered plant community composition. If the primary management goal is to enhance understory cover while promoting native species abundance, our study suggests that mastication may be the most effective treatment strategy in these upland piñon–juniper woodlands. Seed applications and wildlife exclosures further enhanced herbaceous cover following fuel-reduction treatments.     

Land Use and Climate Variability Amplify Carbon,Nutrient, and Contaminant Pulses: A Review with Management Implications

Nonpoint source pollution from agriculture and urbanization is increasing globally at the same time climate extremes have increased in frequency and intensity. We review >200 studies of hydrologic and gaseous fluxes and show how the interaction between land use and climate variability alters magnitude and frequency of carbon, nutrient, and greenhouse gas pulses in watersheds. Agricultural and urban watersheds respond similarly to climate variability due to headwater alteration and loss of ecosystem services to buffer runoff and temperature changes. Organic carbon concentrations/exports increase and organic carbon quality changes with runoff. Nitrogen and phosphorus exports increase during floods (sometimes by an order of magnitude) and decrease during droughts. Relationships between annual runoff and nitrogen and phosphorus exports differ across land use. CH₄ and N₂O pulses in riparian zones/floodplains predominantly increase with: flooding, warming, low oxygen, nutrient enrichment, and organic carbon. CH₄, N₂O, and CO₂ pulses in streams/rivers increase due to similar factors but effects of floods are less known compared to base flow/droughts. Emerging questions include: (1) What factors influence lag times of contaminant pulses in response to extreme events? (2) What drives resistance/resilience to hydrologic and gaseous pulses? We conclude with eight recommendations for managing watershed pulses in response to interactive effects of land use and climate change.     

Effects of Land Use and Climate Change on Stream Temperature II: Threshold Exceedance Duration Projections for Freshwater Mussels

We developed a stochastic hourly stream temperature model (SHSTM) to estimate probability of exceeding given threshold temperature (T) for specified durations (24 and 96 h) to assess potential impacts on freshwater mussels in the upper Tar River, North Carolina. Simulated daily mean stream T from climate change (CC) and land‐use (LU) change simulations for 2021‐2030 and 2051‐2060 were used as input to the SHSTM. Stream T observations in 2010 revealed only two sites with T above 30°C for >24 h and Ts were never >31°C for more than 24 h at any site. The SHSTM suggests that the probability, P, that T will exceed 32°C for at least 96 h in a given year increased from P = 0, in the 20th Century, to P = 0.05 in 2021‐2030 and to P = 0.14 in 2051‐2060. The SHSTM indicated that CC had greater effects on P for 24 and 96 h durations than LU change. Increased P occurred primarily in higher order stream segments in the downstream reaches of the basin. The SHSTM indicated that hourly stream T responded to LU change on the daily scale and did not affect stream T for durations >24 h. The SHSTM indicated that known thermal thresholds for freshwater mussels could be exceeded within the next 50 years in many parts of the upper Tar River basin in North Carolina, which could have negative consequences on the recruitment of freshwater mussels.