Thursday, Dec 7, 2023

The Impact of Mechanical Dewatering on Aquatic Vegetation Management

Whether you’re involved in an aquatic vegetation management program or simply interested in reducing the effects of pollution on your lake, mechanical dewatering should be considered. Dewatering can have some effects, including reducing algae growth and encouraging the growth of aquatic weeds. While the impact of dewatering is often a negative one, it can also serve as a benefit to some fish species and invertebrates.

Reducing Nutrients and Algae in the Water

Using mechanical dewatering for aquatic vegetation management can improve water clarity, reduce nutrient and algae loads, and improve overall water quality. Although this method is not new, it can augment existing aquatic plant control efforts.

While lowering the water level in a lake can improve its overall health, there are better solutions than this. For example, some studies suggest poorly controlled drawdowns can decrease macrophyte density and biomass. In addition, studies have shown that reflooded sediments can improve nitrification and microbial activity for a short period. However, the available water volume typically limits this type of nutrient pulse.

Although this technique is not a panacea, it is one of the most effective methods for controlling nuisance aquatic plants. Lowering the water level by several feet exposes the bottom sediments, creating a natural disturbance regime.

Lowering Water Levels 

During a lake drawdown, water levels are reduced to help remove excessive vegetation. This helps increase water holding capacity and improves fish spawning habitat. A drawdown can occur once or twice per year. The drawdown helps to restore emergent plant communities, which may have been lost during previous years.

Water level drawdown is a common practice in reservoir management. Water level fluctuations influence the survival of numerous species in the littoral zone.

These changes create spatial heterogeneity and structure littoral zone communities. In addition, the inter-annual fluctuations of water levels create a natural disturbance regime. Some species may survive, while others may not. Water level fluctuations also increase or decrease the size of areas where invasive plants can be stranded.

Invertebrates Tolerate Freezing 

Various environmental variables influence the composition of benthic invertebrate assemblages. Some examples include the physical features of the lake, land use, chemical quality, and changes in the hydrologic regime. Other factors include predators, prey, and macrophyte structural composition. In addition, species’ resilience is influenced by their life history strategies and habitat preferences.

Water level fluctuations affect benthic invertebrate food resources and habitat conditions. Increasing winter drawdowns may affect species in the pelagic and sublittoral zone. They increase exposure to freezing and desiccation. These stressors increase assemblage mortality.

The annual winter drawdown regime affects the composition of benthic invertebrates in lakes undergoing dewatering. The most vulnerable species are those in the upper littoral. Feeding generalists are not affected. Species in the pelagic and sublittoral zones have less exposure to drawdowns.

Reducing Algae in The Water 

Managing aquatic weeds is important to protect human and environmental interests. However, these invasive plants can have a detrimental impact on aquatic ecosystems and water quality. In addition, they can pose a threat to fish and humans.

Aquatic weeds have a complex life cycle, which makes them difficult to control. To successfully control these weeds, you must understand their reproductive strategy. Then, you can use chemical, mechanical, or biological methods to control them.

For example, aeration systems can be used for aquatic weed control. These systems provide aeration and can help prevent fish kills, increase water clarity, and promote beneficial algae growth. However, it is important to design the system properly to account for the size of the water body.

Reducing Algae in The Water 

Having low levels of algae in the water can benefit the recruitment of some fish species. However, a more comprehensive study is needed to quantify the magnitude of cascading impacts within trophic structures fully.

The best way to accomplish this is through multiple management approaches. For example, reducing land-based nutrient inputs may be the key to reviving coral populations. Other methods include reducing fine sediment, enhancing habitat quality, and improving water quality.

It’s hard to deny that algae can multiply in waterways with an overabundance of phosphorus. This is especially true in nearshore habitats prone to sediment entrainment during heavy wind and wave action. Some algae species can grow in clumps and even float.