The summer season is the most trying time when it comes to managing the health and beauty of community ponds. During periods of hot and dry weather, the water level in most ponds begins to drop due to lack of runoff and increased evaporation. This creates shallow areas that encourage the growth of problematic algae and aquatic weeds. Shallow, stagnant water also provides prime habitat for the production of mosquito larvae. These problems are magnified in ponds without supplemental aeration such as surface fountains or bottom diffused aeration systems.
Increased summertime water temperatures also reduce the ability of a pond to hold dissolved oxygen. Maintaining adequate dissolved oxygen levels are critical for the survival of fish and mollusks. Oxygen deficits also inhibit the processes of beneficial pond microbes, resulting in increased algae growth and delayed decomposition of recently treated algae.
Oxygen related fish kill
The amount of dissolved oxygen in a pond is influenced by degree of sunlight, water clarity, wave action, and time of day. Under normal summer conditions, we have plenty of sunlight penetration into the water. Direct sunlight allows natural phytoplankton to produce oxygen through photosynthesis. However, a few cloudy days in a row combined with extreme heat causes the dissolved oxygen level to drop. Dissolved oxygen also fluctuates on a daily basis. Oxygen levels are highest in late afternoon after several hours of direct sunlight. Conversely, they are lowest just before the sun rises. Un-managed ponds with excessive algae or aquatic weed growth have the most significant 24-hour dissolved oxygen fluctuations. These types of ponds are at highest risk of fish kills.
Summer weather often brings unwanted pests that are typically absent during cooler times of the year. These include hard to control species such as lyngbya and blue-green algae. Both of these create dense floating mats that are unsightly and produce bad odors. Excessive blooms of blue-green algae are toxic and can potentially kill fish and wildlife. These problematic algae are most common in storm-water ponds with high nutrients due to urban fertilizer runoff. It is ironic that the commercial products that make your lawn so lush and green are the same products that make your pond green and smelly.
Pesky growth of summertime Lyngbya
Extreme care should be taken when applying algaecides and herbicides during the summer. As mentioned, un-aerated ponds hold very little dissolved oxygen and fish often ride a fine line between life and death. The chemical treatment of algae and aquatic vegetation further reduces the oxygen levels in a pond. Although the products themselves do not harm fish, the decomposing material left behind strips valuable oxygen from the water column. Therefore, treating large areas of algae or vegetation under summertime conditions can tip the oxygen balance below the critical level. In order to avoid an oxygen depletion under these conditions, products must be applied in sections. Each partial treatment should be spaced 10-14 days apart. We often recommend halting all algae and aquatic weed treatments during extended periods of 100-degree weather with little or no wind. Unfortunately, these are the same weather conditions that fuel the out-of-control growth of noxious algae. But it is better to temporarily deal with the eyesore than face a pond full of dead, smelly fish. This decision is certainly best for the long-term health of your pond.
A professional pond management program will greatly reduce the risk of encountering some of these problems. However, you as a community can help as well. Here are a few things you can do to assist your pond management provider in maintaining your pond amenities during North Texas summers:
- Halt or reduce all landscape fertilizer applications in the watershed
- Bag all grass clippings in the community
- Do not mow or weed eat all the way down to the pond edge
- Preserve native, aquatic vegetation in moderation
- Adjust fountain/aerator timers to come on earlier than usual in the morning and go off later at night
- Prohibit feeding of waterfowl and other wildlife
- Clean up after pets