Bioretention systems are important tools for capturing and infiltrating polluted runoff, but more data are needed on their effectiveness within Mediterranean climates. A two-year study investigated water retention and pollutant loading in the Ballona Creek Rain Garden during 28 storms. This system was constructed to infiltrate runoff from light industrial and commercial operations bordering the Creek. Study goals were to measure flows and pollutant concentrations in runoff entering and leaving the garden and integrate these to calculate mass loading. Nine pollutants were measured at all flowing inlets/outlets two to three times per storm. Infiltration rates ranged from 18% to 100% and averaged 74% across 28 storms. Average pollutant retention across all nine pollutants for all nine sampled storms was 71.6%. Results demonstrate that bioretention systems can be effectively used in urban Mediterranean climates to promote infiltration, capture pollutants, and prevent polluted stormwater from reaching impaired water bodies.

In August 2023, we conducted a fish survey around Platform Holly and at two nearby seep tents, in southern California, using a remotely operated vehicle. We divided the structures into four habitats: Platform Holly midwaters, Platform Holly base, seep tents towers, and seep tents bases. The platform and the seep tents are similar in the following ways: 1) all are fabricated of steel, 2) all are in approximately the same bottom depth, 3) all are physically close together (and thus in the same water mass and likely exposed to the same current patterns), and 4) all were surveyed within a three-day period using the same methodology. They differ in that, compared to the other three habitats, the seep tent bases are more complex, having numerous ledges and holes. Over all four habitats, we observed a minimum of 36 fish species, representing 6,541 individuals and, at all habitats, the vast majority of fishes were rockfishes (Sebastes spp.). In addition, most of the fishes were small, and the majority at all sites, were juveniles. However, unlike at the other habitats where only juveniles were found, at the more complex seep tents bases we observed large, mature fishes of several species (e.g., copper and vermilion rockfishes). Based on these observations, we hypothesize that adding complexity to the bottom of Platform Holly, as part of the decommissioning process, will increase the density of large, mature fishes, particularly of those species that are usually associated with sheltering sites.