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Salt marsh vegetation provides the structure that supports key wetland functions and the success of wetland restoration efforts depend on the establishment of vegetation, which can take decades. Field experiments aimed at identifying the factors that limit the colonization rate of marsh vegetation can be useful for guiding restoration efforts. We used field experiments and additional measurements to determine the causes for persistently low vegetation cover in a restored salt marsh in southern California. First, we characterized the soil properties of the marsh and found that high salinity and low soil moisture increased with elevation and improved with vegetation. Using this information, we conducted two field experiments—one in the high marsh and the other in the mid marsh to determine the effectiveness of different remedial actions (e.g. irrigation, soil decompaction, soil amendments, and planting and seeding different species) on increasing vegetation cover; the mid marsh experiment evaluated planting and seeding only. In the high marsh, plantings increased cover, and irrigation in combination with soil decompaction facilitated natural plant establishment. In the mid marsh, increases in vegetation cover varied by species planted. In both experiments, the marsh dominant (Salicornia pacifica) naturally recruited, increasing cover whereas seeding did not increase cover. In general, the magnitude and pace of vegetation growth was greater in the mid marsh relative to the high marsh that received less tidal inundation. Collectively, our results show how information gained from experiments conducted during wetland restoration can inform the processes underlying the establishment of vegetation. [ABSTRACT FROM AUTHOR]

Biosolarization is a fumigation alternative that combines solarization with organic amendments to suppress pests and pathogens in agricultural soils. The generation of volatile biopesticides in the soil, stemming from biodegradation of carbon-rich amendments, contributes to pest inactivation. The purpose of this study was to (1) profile volatiles that may contribute to pest control under field conditions and (2) measure volatile compounds that may present nuisance or exposure risks for humans near biosolarized fields where larger-scale anaerobic degradation of residues occurs. Biosolarization was performed using prominent agricultural waste products, hulls and shells from several almond varieties as soil amendments. After 8 days of biosolarization, soil samples were analyzed using solid phase microextraction-gas chromatography coupled to mass spectrometry. Volatile fatty acids and ketones made up 85% of biosolarized soil headspace, but terpenes, alcohols, aldehydes, esters, and sulfides were detected as well. Different almond variety residues produced distinct volatile profiles, and nonpareil-amended soils had a much richer and more diverse profile, as well as a fivefold greater VOC abundance, than pollinator-amended soil. Identified volatiles with low US recommended exposure limits were quantified via internal and external standards, including acetic acid, 2-butanone, butanal, hexanal, and phenylethyl alcohol. Across biosolarization treatments, headspace concentrations of selected compounds did not exceed 1 mg/m3. This study demonstrates that almond processing residues recycled into the soil as biosolarization substrates produce a high diversity of bioactive degradation compounds on a field scale, with low potential of non-target risks to humans. Implications: This manuscript has implications for two policy goals in the state of California: to reduce landfill disposal of organic waste, and to reduce emissions from soil fumigants. Almond hulls and shells are an increasing source of organic waste, and novel recycling strategies must be developed. Here, recycling almond residues as soil amendments promoted the rapid formation of VOCs which may act as alternatives to chemical fumigants. Headspace concentrations of potentially deleterious VOCs produced from treated soil were low, on the order of parts per billion. These results will help achieve policy goals by expanding waste usage and fumigation alternatives. [ABSTRACT FROM AUTHOR]

The occurrence of Escherichia coli O157 and Salmonella spp. in solid bovine manure was investigated through a multi‐county survey in California. Solid bovine manure samples (n = 91) were collected from 13 dairy farms located in multiple counties in California between June 2016 and August 2017. To quantify pathogens, DNA was extracted from bacteria in manure samples. Afterwards, the prevalence and levels of E. coli O157 and Salmonella spp. in solid bovine manure were determined by real‐time quantitative PCR (qPCR). The prevalence of E. coli O157 and Salmonella spp. in solid bovine manure was 15·4 and 6·6% respectively. Escherichia coli O157 and Salmonella spp. levels in positive samples ranged from 3·1 to 5·3 log CFU per g and from positive (the population was <3 log CFU per g) to 5·2 log CFU per g respectively. Surface samples of manure piles had higher prevalence and levels of E. coli O157 and Salmonella spp. than subsurface samples, while no seasonal effects on pathogen occurrence were observed. Our results indicated that solid bovine manure is a source of E. coli O157 and Salmonella spp. and the application of untreated manure as biological soil amendments may pose potential risks to public health. Significance and Impact of the Study: Our findings suggested that the presence of Escherichia coli O157 and Salmonella spp. in solid bovine manure may pose potential risks if untreated manure is applied as biological soil amendments. Considering the large‐scale sampling used in this study, the observations provide a holistic assessment in terms of pathogen prevalence in solid bovine manure. [ABSTRACT FROM AUTHOR]

• Compost amendments to tilled row crop increased SOM contents. • Long-term compost input enhanced macroaggregate formation. • Long-term compost input was associated with higher fungal populations. • Biochar addition had little impact on C dynamics and microbial communities. Soil organic amendments in agricultural production can benefit crop production and a wide range of soil properties, including soil aggregation. Soil aggregate formation is largely driven by microbial activities, and can in-turn influence microbial communities by generating distinct microbial habitats, as well as associated impacts on water and nutrient dynamics. We investigated the long-term effects of two fertilizer management strategies (poultry manure compost vs. mineral fertilizer) and biochar amendment (0 vs. 10 t ha−1 walnut shell biochar, 900 °C pyrolysis temperature, by-product of gasification) on soil aggregation, soil organic C, and microbial community dynamics in water-stable aggregate fractions in corn-tomato rotations. Using wet-sieving, soils (0–15 cm) were divided into four size fractions: large macroaggregates (2000–8000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm) and silt and clay (<53 μm) for calculation of mean weight diameter in both 2014 and 2018. The total C and microbial community composition and abundance within each fraction were evaluated in 2018. Across all treatments, six years of continuous compost application maintained soil aggregate stability and C storage by increasing soil microbial biomass and associated dissolved organic C. Bacterial and fungal populations under compost treatments were significantly higher than under mineral fertilizer treatments based on 16S rRNA gene copy number and internal transcribed spacer (ITS) abundance, which likely contributed to the formation and maintenance of macroaggregates in compost treatments. Interestingly, continuous application of manure compost may increase microbial available C sources by increasing the abundance of bacteria with the potential to degrade aromatic C as predicted from 16S sequences. Soil under the mineral fertilizer treatment showed decreases in the proportion of large macroaggregates, bulk soil C, and aggregate-associated C storage compared to the compost treatment. The application of highly recalcitrant walnut shell biochar had limited long-term impacts on soil aggregation and C dynamics, likely due to its lack of microbially-available C and limited interaction with the soil environment. Our results indicate that continuous compost inputs maintained soil structure and associated physical stabilization of SOM by enlarging soil microbial available C pool, higher soil microbial biomass, and increasing aggregate formation. The soil aggregate structure, in-turn, generated diverse habitats and altered soil microbial communities. Compost inputs, in addition to or in partial replacement of mineral fertilizer inputs, can provide valuable microbial-driven ecosystem services, such as carbon storage and soil structure, while still providing fertility for crop growth. [ABSTRACT FROM AUTHOR]

Mercury mining and its use in gold mine operations left a legacy of contamination in northern California. Contaminated sediments and water continue to affect local and downstream ecosystems. To assess the efficacy of biochar-amended soils on decreasing Hg transport, biochar was used to amend rock and sediment columns and mesocosms to decrease suspended sediment and associated mercury (Hg) in storm water runoff from Sierra Nevada hydraulic mines. Mercury-contaminated storm water runoff and hydraulic mine debris were collected from two hydraulic mine sites in the Yuba River, California watershed. Mercury concentrations and turbidity were analyzed from storm water samples and hydraulic mine debris in three simulated storm runoff experiments using decomposed granite columns, sediment columns, and sediment mesocosms amended at 0%, 2%, or 5% biochar by weight. Columns containing hydraulic mine debris and mixed with 5% biochar had a significant (p < 0.05) reduction in filter-passed mercury (FHg) in the outflow as compared to control columns. To simulate saturated hydraulic mine debris runoff, mesocosms were filled with mine sediment and saturated with deionized water to generate runoff. Five percent biochar in mesocosm trays decreased FHg significantly (p < 0.001), but, because of the angle of the tray, sediment also moved out of the trays. Biochar was effective at reducing FHg from hydraulic mine discharge. Biochar in laboratory columns with decomposed granite or mine sediments was more effective at removing Hg than mesocosms. [ABSTRACT FROM AUTHOR]

Abstract: The results of five years of post-treatment monitoring following in-situ activated carbon (AC) placement for stabilization of polychlorinated biphenyls (PCBs) at an inter-tidal mudflat adjacent to Hunters Point Shipyard, San Francisco Bay, CA, USA are reported in this paper. After five years, AC levels of the sediment cores were comparable to those at earlier sampling times. Passive sampler uptake validated the benefit of the AC amendment with a strong local sorbent dose–response relationship. The PCB uptakes in passive samplers decreased up to 73% with a 3.7 dry wt.% AC dose after five years, confirming the temporal enhancement of the amendment benefit from a 19% reduction with a 4.4% dose observed within one month. The long-term effectiveness of AC, the local AC dose response, the impact of fouling by NOM, the spatial heterogeneity of AC incorporation, and the effects of advective sediment pore-water movement are discussed with the aid of a PCB mass transfer model. Modeling and experimental results indicated that the homogeneous incorporation of AC in the sediment will significantly accelerate the benefit of the treatment. [Copyright &y& Elsevier]

Tidal wetlands can be important sources of methylmercury (MeHg) in aquatic ecosystems. As a result wetland restoration could increase MeHg concentrations. Previous research has shown that addition of Fe[II] to wetland sediment can reduce MeHg production by decreasing concentrations of bioavailable Hg complexes with dissolved sulfur species. In this study, the potential for reducing MeHg production via an iron amendment was evaluated in laboratory microcosms that used intact sediments from a tidal marsh in San Francisco Bay. The micracosms were maintained under simulated tidal conditions and amended at four iron doses (0, 180, 360, and 720 g-Fe/m²). Two experiments were conducted: one with devegetated sediments and one with live wetland vegetation. Following iron addition to the devegetated sediments, porewater S[-II] concentrations decreased for each dose relative to the control with the average weekly export of MeHg in the surface water decreased by 82% and 89% for the two highest doses, respectively. Despite substantial variability within treatment groups, similar trends were observed for the vegetated microcosms. The results suggest that iron addition has the potential to provide a landscape-scale control on MeHg released by restored tidal wetlands; however, additional research is required to evaluate the efficacy of this approach under field conditions. [ABSTRACT FROM AUTHOR]

Abstract: Application of organic soil amendments to disturbed soil has been shown to improve aggregate stability and reduce soil susceptibility to erosion. Employing ultrasonic aggregate stability assessment techniques described earlier [Fristensky, A. and Grismer, M.E., 2008. A simultaneous model for ultrasonic aggregate stability assessment. Catena, 74: 153–164.], we assess the effect of two experimental organic soil amendments – a compost and a woodchip mulch incorporated at a rate of 2000–6000kg ha−1 N-equivalence – on soil aggregation and aggregate stability at four drastically disturbed sites within the Lake Tahoe Basin, USA. Experimental plots were established 1–3years prior to testing. The soils were of granitic or volcanic origin, and disturbed by either ski run or road development. Soil treatments were observed to significantly (p <0.05) increase both aggregation (300% average increase) and ultrasonic aggregate stability (600% average increase) relative to the untreated soil. However, at the two sites disturbed by ski run development, the control treatment (tilling and surface application of pine–needle mulch) performed comparably to the two incorporated compost treatments, suggesting that the effects of the experimental amendments on aggregation were negligible at these sites, or their effective duration was shorter than the evaluation period. Rainfall simulations (72–120mm h−1) were performed on the treatment plots, and results were compared with the ultrasonic aggregate stability indices. Significant (p <0.05) positive correlations were obtained between the measurements of aggregate instability and indices of soil susceptibility to runoff, including steady-state infiltration rate (measured values between 1 and 120mm h−1), and the level of kinetic energy of applied rainfall at which runoff commences (EBR, measured values between 12 and 224J m−2). However, no correlation was found between the ultrasonic aggregate stability indices and observed soil erosion variables. Interestingly, positive relationships (p <0.05) were observed between both infiltration rate and EBR and the proportion of 2–20μm and <2μm particles liberated from the largest aggregates detected in each soil. Our results suggest that ultrasonic aggregate stability indices may be useful indicators of soil susceptibility to runoff and erosion under rainfall. [Copyright &y& Elsevier]

There is renewed interest in the use of nitrate to treat the profundal zone of lakes to inhibit anaerobic biogeochemical processes that result in the degradation of bottom water quality (e.g., sediment phosphorus release, mercury methylation). In this study we used experimental sediment–water interface chambers to quantify the rate of sediment nitrate uptake (SNU) in profundal sediments from Lake Perris, a eutrophic raw water reservoir in Southern California. Deoxygenated chamber water was spiked with nitrate, and nitrate concentration was monitored over time under quiescent conditions, followed by mixed conditions with average water velocities of 1 cm/s. Key findings included: (1) SNU decreased with decreasing nitrate concentration, (2) SNU was higher under mixed versus quiescent conditions by nearly 50%, and (3) nitrate uptake as a function of nitrate concentration followed a conventional sediment oxygen demand model in which nitrate uptake was proportional to the square root of nitrate concentration. The probable mechanism for elevated SNU under mixed conditions was an increased diffusional concentration gradient combined with a decrease in the diffusional boundary layer at the sediment–water interface, both of which enhanced the flux of nitrate from overlaying water into sediment. Managers planning to implement lake nitrate addition should account for induced nitrate demand when determining dosing rates. For example, based on our modeling efforts from this data set, SNU in Lake Perris could range by an order of magnitude, from around 12 mg N/m2/d under quiescent, low nitrate conditions (0.1 mg N/l) to around 120 mg N/m2/d under mixed, high nitrate conditions (5 mg N/l). [ABSTRACT FROM AUTHOR]

Selected nutrient amendments were evaluated for their capacity to enhance growth and nutrition of established but stunted Jeffrey pine ( Pinus jeffreyi Grev. & Balf.) saplings on an acidic Sierra Nevada surface mine. The amendments were applied by topdressing at three rates each and consisted of Forestcote 22-4-6 + Minors, a controlled-release formulation; Free Flow 29-3-4 and Hydro Agri 21-7-14, two conventional fertilizers, with the former featuring urea as the predominant N source, whereas that for the latter was exclusively ammoniacal and nitrate forms; and Milorganite 6-2-0 + Iron, an organic amendment based on municipal biosolids. All formulations reinvigorated sapling growth, generally more so as the amounts supplied increased, with the Free Flow and Hydro Agri amendments marginally more stimulative than Forestcote and Milorganite. Foliar analysis revealed that fertilized saplings had more N, with concentrations that generally rose with amounts supplied, and P but less Mn and Al than the control. Enhanced N nutrition in particular but also that of P probably accounted for most of the growth stimulation by the amendments, as availability of both in the soil was limiting. Of the two metallic elements, reduced Mn was likely most critical because concentrations encountered here were exceedingly elevated overall, including that in the soil, although soil Al was also high. These results suggest that a variety of nutritional amendments can be employed in forest restoration on surface mine sites and those similarly degraded, including sites for which dry climates greatly influence the selection of remedial practices. [ABSTRACT FROM AUTHOR]

The world's ecosystems are experiencing simultaneous changes in the supply of multiple limiting resources. Two of these, water and nitrogen (N) can strongly limit grassland production and can affect community composition and biogeochemical cycles in different ways. Grassland ecosystems in California may be particularly vulnerable to current and predicted changes in precipitation and N deposition, and ecosystem responses to potential interactive effects of water and N are not well understood. Here, we show strong colimitation of plant production resulting from factorial addition of water and N. In addition, water and N addition in combination led to increased dominance of the two most abundant grass species, while N addition regardless of water availability led to decreased species diversity. Late season carbon (C) flux response to water addition depended on N. Only plots that received additional water, but not N, still showed net ecosystem C uptake at the end of the experiment. Our results suggest that grassland ecosystem response to N deposition will be strongly dependent on future precipitation patterns. [ABSTRACT FROM AUTHOR]