Agricultural conservation practices in Iowa watersheds: comparing actual implementation with practice potential.

As part of the solution to reduce the size of the Gulf of Mexico hypoxia, the state of Iowa has created the Iowa Nutrient Reduction Strategy (INRS) to reduce total nitrogen and phosphorous loads by 45% by 2035. A major component of the strategy is implementation of conservation practices to reduce loads of non-point source pollution from agricultural lands. To identify potential locations for conservation practices in Iowa watersheds, the Agricultural Conservation Planning Framework (ACPF) is being used. In addition, the location of existing implemented practices are being identified by the Iowa Best Management Practices Mapping Project (IBMP). From these two products, a methodology was developed to compare the differences between actual implementation and practice placement potential. The compared conservation practices are grassed waterways, wetlands and ponds, and water and sediment control basins (WASCOBs). The comparison is performed in three hydrologic unit code 12 (HUC-12) watersheds in three distinct landform regions of Iowa. Analyses show that grassed waterways are widely implemented (at least 78% of the potential) in the three watersheds. For ponds and wetlands, the majority of the existing structures were smaller than the ACPF potential wetlands (average drainage area between 7 and 20 ha compared to between 89 and 109 ha). WASCOB implementation was only present in one watershed, most likely due to regional differences in conservation preferences. Coupled together the IBMP and ACPF will be important for stakeholders of watersheds in planning future investment and advancing towards a more systems-based approach to conservation.

Fish navigation of large dams emerges from their modulation of flow field experience.

Navigating obstacles is innate to fish in rivers, but fragmentation of the world's rivers by more than 50,000 large dams threatens many of the fish migrations these waterways support. One limitation to mitigating the impacts of dams on fish is that we have a poor understanding of why some fish enter routes engineered for their safe travel around the dam but others pass through more dangerous routes. To understand fish movement through hydropower dam environments, we combine a computational fluid dynamics model of the flow field at a dam and a behavioral model in which simulated fish adjust swim orientation and speed to modulate their experience to water acceleration and pressure (depth). We fit the model to data on the passage of juvenile Pacific salmonids (Oncorhynchus spp.) at seven dams in the Columbia/Snake River system. Our findings from reproducing observed fish movement and passage patterns across 47 flow field conditions sampled over 14 y emphasize the role of experience and perception in the decision making of animals that can inform opportunities and limitations in living resources management and engineering design.

Antecedent moisture controls on stream nitrate flux in an agricultural watershed.

Evaluating nitrate-N fluxes from agricultural landscapes is inherently complex due to the wide range of intrinsic and dynamic controlling variables. In this study, we investigate the influence of contrasting antecedent moisture conditions on nitrate-N flux magnitude and dynamics in a single agricultural watershed on intra-annual and rainfall-event temporal scales. High temporal resolution discharge and nitrate concentration data were collected to evaluate nitrate-N flux magnitude associated with wet (2009) and dry (2012) conditions. Analysis of individual rainfall events revealed a marked and consistent difference in nitrate-N flux response attributed to wet/dry cycles. Large-magnitude dilutions (up to 10 mg N L) persisted during the wet antecedent conditions (2009), consistent with a dominant baseflow contribution and excess groundwater release in relation to precipitation volume (discharge > > precipitation). Smaller-magnitude concentrations (<7 mg N L) were observed during the drought conditions of 2012, consistent with a quickflow-dominated response to rain events and infiltration/storage of precipitation resulting in discharge < precipitation. Nitrate-N loads and yields from the watershed were much higher (up to an order of magnitude) in the wet year vs. the dry year. Our results suggest that the response of nitrate-N loading to rain events is highly dependent on intra-annual antecedent moisture conditions and subsurface hydrologic connectivity, which together dictate the dominant hydrologic pathways for stream recharge. Additionally, the results of our study indicate that continued pronounced wet/dry cycles may become more dominant as the short-term driver of future nitrate-N exports.

Estimating Iowa's riverine phosphorus concentrations via water quality surrogacy.

Phosphorus (P) is a widespread waterborne pollutant that impairs many waterbodies. However, it is challenging to measure directly, and much research has been dedicated to developing surrogacy models that can repeatedly predict its concentration. Optimal approaches for modeling strategies are often unclear and depend upon local P dynamics and the availability of financial and technical resources. This study presents a schema for developing P surrogacy models at a statewide scale (16 major rivers in Iowa, USA). Specifically, we examined the relationship between particulate phosphorus (Part P) and orthophosphate (OP) and explored the viability of eight potential surrogates in predicting their concentrations using multiple linear regression and power regression methods. We also investigated similarities between surrogate models for Part P and total suspended solids (TSS). At all sites, OP and Part P were not strongly correlated (mean R = 0.20 ± 0.17). Many instances were observed where samples had high concentrations of one form but not the other. Modeling results demonstrated that turbidity was consistently the best predictor (t-statistics >10) of Part P, and adding other surrogates alongside turbidity did little to improve model performance. No surrogates proved useful in estimating OP. Viable power regression models were created using turbidity to predict Part P (mean R2 = 0.69 ± 0.12). These models had a nonlinear form where Part P concentrations leveled off as waters became exceptionally turbid. This contrasted with TSS, which maintained a strong linear relationship across all turbidity levels. Turbidity-based models show promise in quantifying statewide P levels, as they enable high-resolution and real-time Part P estimates.

Iowa stream nitrate and the Gulf of Mexico.

The main objective of this work was to quantify and update the U.S. Midwest agricultural state of Iowa's contribution of nitrate-nitrogen to the Mississippi River stream network against the backdrop of the ongoing problem of Gulf of Mexico hypoxia. To achieve this objective, we used stream nitrate and discharge data collected from 1999 until 2016 at 23 Iowa stream sites near watershed outlets, along with publicly-available data for sites downstream of Iowa on the Missouri and Mississippi Rivers. Our analysis shows that Iowa contributes between 11 and 52% of the long-term nitrate load to the Mississippi-Atchafalaya Basin, 20 to 63% to the Upper Mississippi River Basin, and 20 to 89% to the Missouri River Basin, with averages of 29, 45 and 55% respectively. Since 1999, nitrate loads in the Iowa-inclusive basins have increased and these increases do not appear to be driven by changes in discharge and cropping intensity unique to Iowa. The 5-year running annual average of Iowa nitrate loading has been above the 2003 level for ten consecutive years, implying that Gulf hypoxic areal goals, also based on a 5-year running annual average, will be very difficult to achieve if nitrate retention cannot be improved in Iowa. An opportunity exists for land managers, policy makers and conservationists to manifest a positive effect on water quality by targeting and implementing nitrate reducing-practices in areas like Iowa while avoiding areas that are less likely to affect Gulf of Mexico hypoxia.

Can north american fish passage tools work for South american migratory fishes?

In North America, the Numerical Fish Surrogate (NFS) is used to design fish bypass systems for emigrating juvenile salmon as they migrate from hatchery outfalls and rearing habitats to adult habitat in the oceans. The NFS is constructed of three linked modules: 1) a computational fluid dynamics model describes the complex flow fields upstream of dams at a scale sufficiently resolved to analyze, understand and forecast fish movement, 2) a particle tracking model interpolates hydraulic information from the fixed nodes of the computational fluid model mesh to multiple locations relevant to migrating fish, and 3) a behavior model simulates the cognition and behavior of individual fish in response to the fluid dynamics predicted by the computational fluid dynamics model. These three modules together create a virtual reality where virtual fish exhibit realistic dam approach behaviors and can be counted at dam exits in ways similar to the real world. Once calibrated and validated with measured fish movement and passage data, the NFS can accurately predict fish passage proportions with sufficient precision to allow engineers to select one optimum alternative from among many competing structural or operational bypass alternatives. Although South American fish species are different from North American species, it is likely that the basic computational architecture and numerical methods of the NFS can be used for fish conservation in South America. Consequently, the extensive investment made in the creation of the NFS need not be duplicated in South America. However, its use in South America will require that the behavioral response of the continent's unique fishes to hydrodynamic cues must be described, codified and tested before the NFS can be used to conserve fishes by helping design efficient South American bypass systems. To this end, we identify studies that could be used to describe the movement behavior of South American fishes of sufficient...

Na América do Norte, o Numerical Fish Surrogate (NFS) é utilizado no projeto de sistemas de transposição de juvenis de salmão em seus deslocamentos dos habitats de desova e desenvolvimento inicial para o de adultos, no oceano. O NFS é estruturado em três módulos interconectados: 1) um modelo computacional de dinâmica de fluidos (CFD) que descreve o complexo escoamento acima da barragem em uma escala suficientemente apropriada para analisar, entender e prever os movimentos dos peixes, 2) um modelo de rastreamento de partículas que interpola informações hidráulicas dos nós da malha do modelo computacional para localizações múltiplas relevantes ao peixe em migração, 3) um modelo comportamental que simula o conhecimento e o comportamento de cada peixe em resposta à dinâmica do escoamento predita pelo modelo computacional. Esses três módulos juntos criam uma realidade virtual onde peixes virtuais exibem um comportamento realístico de aproximação da barragem e podem ser contados de uma forma similar a do mundo real. Uma vez calibrado e validado com medições do movimento dos peixes e dados de passagem, o NFS pode predizer acuradamente a proporção de passagem de peixes, com suficiente precisão para permitir que engenheiros selecionem uma alternativa ótima dentre as várias opções estruturais e operacionais. Embora as espécies de peixes Sul Americanas sejam diferentes das espécies da América do Norte, é provável que a arquitetura computacional básica e os métodos numéricos do NFS possam ser usados para a conservação de peixes na América do Sul. Consequentemente, o grande investimento feito na criação do NFS não precisa ser repetido na América do Sul. Contudo, seu uso na América do Sul exigirá que a resposta comportamental dessa fauna aos sinais hidrodinâmicos seja descrita, codificada e testada antes que o NFS possa ser usado na conservação de peixes pelo seu emprego na projeção de sistemas de transposição eficientes. Nesse contexto, o presente...