Nearshore concentrations of fecal indicator bacteria (FIB) are controlled by a complex array of physical and biological processes. The studies herein evaluate the contribution of several such process to coastal FIB dynamics using laboratory studies, mathematical modeling, and fieldwork. Two field sites are discussed; Border Fields State Beach (BFSB) and Huntington Beach, both sites of chronic FIB contamination in Southern California. At Huntington Beach field measurements of alongshore currents and horizontal diffusion were used to parameterize a suite of individual based particle tracking models. These models were used diagnostically to evaluate the contribution of physics and mortality to FIB dynamics. Advection and diffusion were found to explain a significant fraction of surfzone FIB decay, but played a lesser role offshore, suggesting that offshore FIB loss may be dominated by mortality rather than physics. No single mechanism was identified that best-explained FIB mortality at this beach, although cross-shore variable mortality mechanisms had higher skill than spatially constant ones. At BFSB the relative contribution of physics and mortality to nearshore FIB dynamics varied temporally rather than in the cross-shore. Generalized linear model analyses at this beach linked FIB contamination to an anthropogenic beach nourishment. Field-based microcosm experiments (using FIB from this source), in combination with surfzone bacterial monitoring, showed that FIB concentrations were controlled by rapid mortality of a "sensitive" FIB fraction and physical dilution/mixing, which became steadily more important as sensitive FIB died off, leaving behind a resistant community. Co-existing populations of sensitive and resistant FIB were also observed in laboratory experiments evaluating the effects of phytoplankton concentration on FIB mortality. Mortality in these experiments was biphasic, with loss of sensitive FIB occurring > 10x faster than resistant FIB. Notably, bloom concentrations of phytoplankton halved mortality rates of both FIB groups, enhancing survivorship. This signal was not obscured by physical transport/mixing (Huntington Beach particle tracking model), suggesting that phytoplankton have the potential to be an important factor controlling FIB concentrations. This dissertation highlights the importance of both physics and biology as factors controlling nearshore FIB and points to phytoplankton communities as an under-evaluated control on FIB growth/mortality in marine systems

Nearshore concentrations of fecal indicator bacteria (FIB) are controlled by a complex array of physical and biological processes. The studies herein evaluate the contribution of several such process to coastal FIB dynamics using laboratory studies, mathematical modeling, and fieldwork. Two field sites are discussed; Border Fields State Beach (BFSB) and Huntington Beach, both sites of chronic FIB contamination in Southern California. At Huntington Beach field measurements of alongshore currents and horizontal diffusion were used to parameterize a suite of individual based particle tracking models. These models were used diagnostically to evaluate the contribution of physics and mortality to FIB dynamics. Advection and diffusion were found to explain a significant fraction of surfzone FIB decay, but played a lesser role offshore, suggesting that offshore FIB loss may be dominated by mortality rather than physics. No single mechanism was identified that best-explained FIB mortality at this beach, although cross-shore variable mortality mechanisms had higher skill than spatially constant ones. At BFSB the relative contribution of physics and mortality to nearshore FIB dynamics varied temporally rather than in the cross-shore. Generalized linear model analyses at this beach linked FIB contamination to an anthropogenic beach nourishment. Field-based microcosm experiments (using FIB from this source), incombination with surfzone bacterial monitoring, showed that FIB concentrations were controlled by rapid mortality of a “sensitive” FIB fraction and physical dilution mixing, which became steadily more important as sensitive FIB died off, leaving behind a resistant community. Co-existing populations of sensitive and resistant FIB were also observed in laboratory experiments evaluating the effects of phytoplankton concentration on FIB mortality. Mortality in these experiments was biphasic, with loss of sensitive FIB occurring > 10x faster than resistant FIB. Notably, bloom concentrations of phytoplankton halved mortality rates of both FIB groups, enhancing survivorship. This signal was not obscured by physical transport/mixing (Huntington Beach particle tracking model), suggesting that phytoplankton have the potential to be an important factor controlling FIB concentrations. This dissertation highlights the importance of both physics and biology as factors controlling nearshore FIB and points to phytoplankton communities as an under-evaluated control on FIB growth/mortality in marine systems.

The discharge of excess nitrogen to streams and rivers poses an existential threat to both humans and ecosystems. A seminal study of headwater streams across the United States concluded that in-stream removal of nitrate is controlled primarily by stream chemistry and biology. Reanalysis of these data reveals that stream turbulence (in particular, turbulent mass transfer across the concentration boundary layer) imposes a previously unrecognized upper limit on the rate at which nitrate is removed from streams. The upper limit closely approximates measured nitrate removal rates in streams with low concentrations of this pollutant, a discovery that should inform stream restoration designs and efforts to assess the effects of nitrogen pollution on receiving water quality and the global nitrogen cycle.

Constructed stormwater wetlands provide a host of ecosystem services, including potentially pathogen removal. We present results from a multi-wetland study that integrates across weather, chemical, microbiological and engineering design variables in order to identify patterns of microbial contaminant removal from inlet to outlet within wetlands and key drivers of those patterns. One or more microbial contaminants were detected at the inlet of each stormwater wetland (Escherichia coli and Enterococcus > Bacteroides HF183 > adenovirus). Bacteroides HF183 and adenovirus concentrations declined from inlet to outlet at all wetlands. However, co-removal of pathogens and fecal indicator bacteria only occurred at wetlands where microbial assemblages at the inlet (dominated by Proteobacteria and Bacteriodetes) were largely displaced by indigenous autotrophic microbial communities at the outlet (dominated by Cyanobacteria). Microbial community transitions (characterized using pyrosequencing) were well approximated by a combination of two rapid indicators: (1) fluorescent dissolved organic matter, and (2) chlorophyll a or phaeophytin a fluorescence. Within-wetland treatment of fecal markers and indicators was not strongly correlated with the catchment-to-wetland area ratio, but was diminished in older wetlands, which may point to a need for more frequent maintenance.

Bedforms are a focal point of carbon and nitrogen cycling in streams and coastal marine ecosystems. In this paper, we develop and test a mechanistic model, the "pumping and streamline segregation" or PASS model, for nitrate removal in bedforms. The PASS model dramatically reduces computational overhead associated with modeling nitrogen transformations in bedforms and reproduces (within a factor of 2 or better) previously published measurements and models of biogeochemical reaction rates, benthic fluxes, and in-sediment nutrient and oxygen concentrations. Application of the PASS model to a diverse set of marine and freshwater environments indicates that (1) physical controls on nitrate removal in a bedform include the pore water flushing rate, residence time distribution, and relative rates of respiration and transport (as represented by the Damkohler number); (2) the biogeochemical pathway for nitrate removal is an environment-specific combination of direct denitrification of stream nitrate and coupled nitrification-denitrification of stream and/or sediment ammonium; and (3) permeable sediments are almost always a net source of dissolved inorganic nitrogen. The PASS model also provides a mechanistic explanation for previously published empirical correlations showing denitrification velocity (N2 flux divided by nitrate concentration) declines as a power law of nitrate concentration in a stream (Mulholland et al. Nature, 2008, 452, 202-205).

Cities in drought prone regions of the world such as South East Australia are faced with escalating water scarcity and security challenges. Here we use 72 years of urban water consumption data from Melbourne, Australia, a city that recently overcame a 12 year "Millennium Drought", to evaluate (1) the relative importance of climatic and anthropogenic drivers of urban water demand (using wavelet-based approaches) and (2) the relative contribution of various water saving strategies to demand reduction during the Millennium Drought. Our analysis points to conservation as a dominant driver of urban water savings (69%), followed by nonrevenue water reduction (e.g., reduced meter error and leaks in the potable distribution system; 29%), and potable substitution with alternative sources like rain or recycled water (3%). Per-capita consumption exhibited both climatic and anthropogenic signatures, with rainfall and temperature explaining approximately 55% of the variance. Anthropogenic controls were also strong (up to 45% variance explained). These controls were nonstationary and frequency-specific, with conservation measures like outdoor water restrictions impacting seasonal water use and technological innovation/changing social norms impacting lower frequency (baseline) use. The above-noted nonstationarity implies that wavelets, which do not assume stationarity, show promise for use in future predictive models of demand.

Green infrastructure (also referred to as low impact development, or LID) has the potential to transform urban stormwater runoff from an environmental threat to a valuable water resource. In this paper we focus on the removal of fecal indicator bacteria (FIB, a pollutant responsible for runoff-associated inland and coastal beach closures) in stormwater biofilters (a common type of green infrastructure). Drawing on a combination of previously published and new laboratory studies of FIB removal in biofilters, we find that 66% of the variance in FIB removal rates can be explained by clean bed filtration theory (CBFT, 31%), antecedent dry period (14%), study effect (8%), biofilter age (7%), and the presence or absence of shrubs (6%). Our analysis suggests that, with the exception of shrubs, plants affect FIB removal indirectly by changing the infiltration rate, not directly by changing the FIB removal mechanisms or altering filtration rates in ways not already accounted for by CBFT. The analysis presented here represents a significant step forward in our understanding of how physicochemical theories (such as CBFT) can be melded with hydrology, engineering design, and ecology to improve the water quality benefits of green infrastructure.

Enclosed beaches along urban coastlines are frequent hot spots of fecal indicator bacteria (FIB) pollution. In this paper we present field measurements and modeling studies aimed at evaluating the impact of small storm drains on FIB pollution at enclosed beaches in Newport Bay, the second largest tidal embayment in Southern California. Our results suggest that small drains have a disproportionate impact on enclosed beach water quality for five reasons: (1) dry weather surface flows (primarily from overirrigation of lawns and ornamental plants) harbor FIB at concentrations exceeding recreational water quality criteria; (2) small drains can trap dry weather runoff during high tide, and then release it in a bolus during the falling tide when drainpipe outlets are exposed; (3) nearshore turbulence is low (turbulent diffusivities approximately 10(-3) m(2) s(-1)), limiting dilution of FIB and other runoff-associated pollutants once they enter the bay; (4) once in the bay, runoff can form buoyant plumes that further limit vertical mixing and dilution; and (5) local winds can force buoyant runoff plumes back against the shoreline, where water depth is minimal and human contact likely. Outdoor water conservation and urban retrofits that minimize the volume of dry and wet weather runoff entering the local storm drain system may be the best option for improving beach water quality in Newport Bay and other urban-impacted enclosed beaches.

Abstract: Natural treatment systems (NTS) for stormwater have the potential to provide a myriad of ecosystem services to society. Realizing this potential requires active collaboration among engineers, ecologists and landscape planners and begins with a paradigm shift in communication whereby these groups are made aware of each other's perceptions about NTS and the presence of knowledge gaps that their respective disciplines can bridge. Here we participate in the first part of what we hope will be a reciprocal exchange: presenting results from a landscape perceptions survey to urban planners, ecologists and landscape architects that illustrates how the next generation of engineers perceives NTS relative to other landscape features, and the implications of those perceptions for future infrastructure development. Our results suggest that although lawns, gardens and native ecosystems were perceived as multifunctional, providing characteristic bundles of services/disservices, perceptions of NTS were more variable (i.e. there was no social norm for their perception). Environmental worldviews, knowledge, attitudes about ecosystem services and demographics were all significant drivers of perceived services. However, students had difficulty identifying NTS correctly, and factual knowledge about NTS did not help students associate NTS with typical design services like flood reduction more than features not designed for those purposes, such as lawns. This suggests that engineering students lack familiarity with the outward appearance of NTS and have difficulty placing NTS services into a broader landscape context. Expertise from urban planning and ecology could help bridge these knowledge gaps, improving the capacity of tomorrow's engineers to co‐design NTS to meet diverse community needs. Read the free Plain Language Summary for this article on the Journal blog.

Stormwater infrastructure substantially impacts water quality and supply. In the U.S., local agency investments rely on public support from taxes or fees. Assessing individuals’ knowledge and willingness to pay helps inform potential pathways to funding and green infrastructure implementation. Using a 2018–2019 survey of 868 University of California students and staff, we analyze stormwater knowledge and willingness to pay or support public fund allocation for green infrastructure, especially natural treatment systems (NTS). Results of three separate regression models, each with a one-campus random sample and an all-campus convenience sample, show the majority of respondents supported allocating personal and campus funds for NTS. Preexisting environmental attitudes (on the New Ecological Paradigm scale) were the most common driver in nearly all models, but with inconsistent results and low explanatory power across models. Harnessing public support to increase stormwater investment may require tailored benefit messaging or other motivational frameworks, particularly in semiarid environments.