North County Lagoons profiled in Historical Ecology study

A fascinating study of the historical ecology of North San Diego County’s six coastal lagoons, including the San Dieguito Lagoon, was published (September 2014) and is available for purchase on the San Francisco Estuary Institute & Aquatic Science Center (SFE) website.

What was the San Dieguito Lagoon like in the late nineteenth century? What uses were most common and how much area did it cover? How has the river changed over time and what events led to its current configuration? Answers to these questions and more are found in this study, funded by the California State Coastal Conservancy, which explores and documents the ecological characteristics of San Diego’s North County lagoons circa the late 1700s to late 1800s and contrasts them to today’s conditions including historical depictions, in-depth analysis, maps, and explanations of lagoon dynamics over time. The study also explores the historic changes in watershed dynamics including water flow, water quality, and lagoon inlet tidal prisms.

San Dieguito Lagoon’s 345 square-mile watershed is by far the largest watershed of the six North County lagoons, four times the next largest watershed (Los Penasquitos) and over 15 times the size of the smallest. Historically, the inlet at San Dieguito was not permanently open to the ocean, instead it was often blocked by a sand bar across the lagoon mouth. During the dry season flows from the river to the ocean ceased and wave action created the accumulation of sand at the mouth. This was exacerbated throughout the first half of the 20th century mostly from the reduction of freshwater flows after the construction of the Hodges Dam. The study’s in-depth analysis of inlet dynamics uses the San Dieguito Lagoon as a case study.

All the north county lagoons are covered extensively providing the historic context for the current state of our unique lagoon systems and a glimpse into early exploration and settlement of the area. The hope is that a better understanding of the historic ecological context and evolution will help guide and better inform restoration and management decisions in the future.