Effect of landscape irrigation regulations on runoff volume from low-density residential catchments during two California droughts.

The severe drought in California (2012-2016) generated significant public and government concern. State and local watering regulations were enacted to reduce residential and commercial water-use during the droughts. This study presents a comparison of residential runoff volumes before and after local landscape irrigation regulations were enacted during the droughts of 2008 and 2012-2016. Each sampling site (Folsom 1 and Folsom 2) was a storm drain outfall that drained a low-density residential catchment in the City of Folsom. Dry season runoff measured at the sampling sites represents neighborhood outdoor water waste, mainly from landscape irrigation. During the drought of 2012-2016, median runoff flows were significantly reduced after local landscape irrigation regulations were enacted. The daily runoff pattern was also highly influenced by regulation, with reductions of daily peak runoff flows on 4-5 days in a week after watering regulations were enacted. The number of peak flow events in the daily runoff pattern were reduced during this period. In addition, a significant reduction in mean runoff volume occurred. Based on these results, the watering regulations enacted by the City of Folsom had a positive effect on reducing urban runoff from residential neighborhoods during the dry season. As the results are from monitoring sites in a relatively small geographical area, further work should evaluate reductions in irrigation runoff from other California locations to determine if this is a localized phenomenon.

The population of oomycetes in a recycled irrigation water system at a horticultural nursery in southern California.

Recapture and recycling of irrigation water is often required to meet enormous water demands at horticultural nurseries. We tested four water types associated with a recycled irrigation system at a commercial container nursery in southern California for presence of oomycete plant pathogens from July 2015 to December 2017. These water types included: the main source of water originating from a reservoir, retention water from an on-site collection pond, irrigation water received by different growing areas within the nursery, and irrigation runoff captured in polyethylene sheet-lined runoff channels. The genera Phytophthora, Pythium, and Phytopythium together contributed more than 85% of the total oomycete population detected in the recycled irrigation system. The Phytophthora and Pythium genera were represented by member species from nine (1-4, 6-10) and eight (A, B, D-F, H-J) different sub-generic clades, respectively. Incoming water sourced from the reservoir was found to harbor known plant pathogens such as Phytophthora citricola-complex, P. capsici-cluster, P. tropicalis,P citrophthora-cluster, P. nemorosa-cluster, P. riparia, P. cryptogea-complex, P. parsiana-cluster, P. sp. nov. aff. kernoviae, Pythium dissotocum-complex, Py. oligandrum-cluster, Py. irregulare, and Phytopythium litorale. Runoff water showed the highest oomycete species richness and frequency of detection with both filtration and leaf baiting methods. In addition to plant pathogens, oomycete fish pathogens such as Aphanomyces laevis, Pythium chondricola-complex, Pythium flevoense-complex, and Saprolegnia diclina-complex were also detected in greater abundance in the recycled irrigation water. The oomycete species richness in the runoff water was correlated with several environmental parameters such as soil temperature. Greater oomycete richness in incoming water was associated with higher soil temperatures, whereas richness in runoff declines with increasing soil temperature, likely suggesting connections to weather-dependent nursery operations.

Role of Sediments in Insecticide Runoff from Urban Surfaces: Analysis and Modeling.

Insecticides, such as pyrethroids, have frequently been detected in runoff from urban areas, and their offsite transport can cause aquatic toxicity in urban streams and estuaries. To better understand the wash-off process of pesticide residues in urban runoff, the association of pyrethroids with sediment in runoff from residential surfaces was investigated in two watersheds located in Northern California (Sacramento County). Rainfall, flow rate, and event mean concentrations/loads of sediments and pyrethroids, collected during seasonal monitoring campaigns from 2007 to 2014, were analyzed to identify relationships among stormwater quality and rainfall characteristics, primarily using Principal Component Analysis (PCA). Pyrethroid wash-off was strongly related to sediment wash-off whenever sediment loads exceeded 10 mg; this value was conveniently selected as a threshold between dissolved and particle-bound control of off-site pyrethroid transport. A new mechanistic model for predicting pyrethroid wash-off profiles from residential surfaces at basin-scale was implemented in the Storm Water Management Model (SWMM). The accuracy of the model predictions was estimated by evaluating the root mean square error (RMSE), Nash⁻Sutcliff efficiency (NSE), and Kling⁻Gupta efficiency (KGE) for each pyrethroid detected (RMSEtot = 0.13; NSEtot = 0.28; KGEtot = 0.56). The importance of particle-bound transport revealed in this work confirms previous field investigations at a smaller scale, and it should be a key consideration when developing policies to mitigate pesticide runoff from urban areas.

Pollutant loading from low-density residential neighborhoods in California.

This paper presents a comparison of pollutant load estimations for runoff from two geographically distinct residential suburban neighborhoods in northern and southern California. The two neighborhoods represent a single urban land use type: low-density residential in small catchments (<0.3 km2) under differing regional climates and irrigation practices. Pollutant loads of pesticides, nutrients, and drinking water constituents of concern are estimated for both storm and non-storm runoff. From continuous flow monitoring, it was found that a daily cycle of persistent runoff that peaks mid-morning occurs at both sites. These load estimations indicate that many residential neighborhoods in California produce significant non-storm pollutant loads year-round. Results suggest that non-storm flow accounted for 47-69% of total annual runoff and significantly contributed to annual loading rates of most nutrients and pesticides at both sites. At the Southern California site, annual non-storm loads are 1.2-10 times higher than storm loads of all conventional constituents and nutrients with one exception (total suspended solids). At the Northern California site, annual storm loads range from 51 to 76% of total loads for all conventional constituents and nutrients with one exception (total dissolved solids). Non-storm yields of pesticides at the Southern California site range from 1.3-65 times higher than those at the Northern California site. The disparity in estimated pollutant loads between the two sites indicates large potential variation from site-to-site within the state and suggests neighborhoods in drier and milder climates may produce significantly larger non-storm loads due to persistent dry season runoff and year-round pest control.