Urban runoff from gardens and hard surfaces is the #1 source of ocean pollution. In that runoff are pollutants such as:
- Synthetic fertilizers - increased nutrients leads to algal blooms and red tides, lowering dissolved oxygen levels enough to kill aquatic habitat and fisheries.
- Pesticides, herbicides and fungicides - poison humans, marine life and soil biology.
- Automobile engine oil, exhaust and brake pad dust as well as exhaust from utilities - poison marine life.
- Bacteria - sicken humans and marine life, and can close beaches.
- Sediment (soil) - the finer material can be laced with heavy metals, and too much sediment can smother coral. Some (larger) sediment transport is needed to maintain streambanks and riverbottoms as well as replenish beaches. (All four of these bullets also contribute to Ocean Acidification (OA), which decreases shell- and skeleton-forming calcium carbonates in the ocean, among other problems. This causes sea life like shell fish and coral to either decline or try to put more energy into gathering carbonates, having less energy to survive. Here's a blog post about OA.)
- Turbidity - per this website, it's the degree to which water "loses its transparency due to the presence of suspended particulates. The suspended particles absorb heat from the sunlight, making turbid waters become warmer, and so reducing the concentration of oxygen in the water (oxygen dissolves better in colder water). Some organisms also can’t survive in warmer water. The suspended particles scatter the light, thus decreasing the photosynthetic activity of plants and algae, which contributes to lowering the oxygen concentration even more. As a consequence of the particles settling to the bottom, shallow lakes fill in faster, fish eggs and insect larvae are covered and suffocated, gill structures get clogged or damaged."
The first one-inch of rain after a dry spell is called the "first flush," and contains most of the pollutants during a rainstorm. Traditional building codes have directed rainwater off the property to prevent flooding of a site. But this runoff contributes to flooding of neighborhoods and erosion of stream banks. It also can overwhelm sewer systems in which the storm drains and sewer infrastructure is combined. Plus, this wastes a free source of irrigation for the landscape. Runoff also happens during dry periods, known as dry-weather runoff, with sprinklers overwatering and overshooting the landscape.
Soil and plants are also part of the solution to climate change mitigation and removing greenhouse gases from the atmosphere such as carbon dioxide.
- Plants absorb carbon dioxide through photosynthesis. The oxygen is released into the air, and the carbon is either used by the plant to build its structure or secreted at carbon chains (sugars) through its roots into soil. The microbiology around the roots eat the sugars, and poop out plant-available food. Some of it gets locked up in soil, holding carbon in soil.
- Soil microbiology helps break down plant roots and other dead plant material, turning it into soil humus, what makes soil have its dark brown color. Soil humus is a stable form of carbon that can be locked up in soil for years.
If soil is disturbed from practices such as tilling or "turning over" soil, the carbon will be oxidized, or exposed to oxygen and released into the atmosphere as carbon dioxide. Also, it's important to allow dead plant materials such as leaves to remain as mulch and organic matter to continue the process of feeding soil microbiology and sequestering carbon.