California Fish Die-off

large fish die-off in California was recently reported.

Large die-offs of fish is not a new phenomena, but one that is disturbingly more common. These die-offs are usually due to hypoxic or anoxic conditions (meaning that there is not enough or no oxygen in the water). Hypoxic and anoxic conditions can be caused by a number of possible stressors on an environment, and not all of them are anthropogenic. Upwelling along coastal areas can bring nutrient rich water up from the bottom of the ocean, leading to anoxic conditions. However, these natural events pale in comparison to man made hypoxic zones. Awareness of the “dead-zone” in the Gulf of Mexico has grown in recent years, but the increase in frequency, location, duration, and size of these “dead-zones” is a global problem.

One of the main causes for these “dead-zones” is the increased nutrient pollution in the water in developed and developing watersheds. Agriculture (and agricultural practices) can be a major source of nutrient pollution (mainly from the application of fertilizers), but studies show that urban development can also lead to increased nutrient loads.  One of the many benefits of urban storm water management (such as rain gardens, eco roofs, and bioswales) is a reduction in the amount of nutrients introduced into waterways from developed land, which can reduce the size, duration, and frequency of hypoxic and anoxic conditions.  Restoring urban streams and riparian zones can also reduce nutrient pollution.

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