Aquatic plants, or macrophytes, play a crucial role in freshwater ecosystems. They provide habitat for wildlife, introduce oxygen into the water, and help remove nutrients. Despite their benefits, these plants are often viewed as a nuisance, particularly by those engaged in swimming, water sports, or whose activities are disrupted by dense vegetation. To address this, many ecosystems experience regular removal of these plants.
A recent study conducted by researchers from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) has examined aquatic plant management in various freshwater environments across five countries. This research highlights that sometimes, the best approach might be to do nothing at all.
Study Findings
The study assessed aquatic plant growth in lakes, rivers, and reservoirs with varying nutrient levels and climates. It focused on submerged, emergent, and free-floating plants, both native and non-native. Published in Science of The Total Environment, the study suggests that while mass growth of aquatic plants can diminish recreational opportunities, it often benefits other ecosystem services.
Aquatic plants grow differently: some float freely, others are rooted with floating leaves, and some are completely submerged. They thrive under conditions of ample nutrients, light, warmth, and minimal disturbances like strong currents or droughts.
Impact of Water Regulation
Regulated water bodies, such as the River Spree in Germany and Lake Kemnader, show how human intervention can affect aquatic plant growth. Regulation often results in slow-moving, nutrient-rich water that promotes plant proliferation. For instance, the River Spree’s regulation has led to an increase in native submerged plants, while Lake Kemnader’s regulation has fostered the growth of non-native narrow-leaved waterweed.
Dr. Sabine Hilt of IGB notes, “Regulation in nutrient-poor, cold rivers can also lead to mass plant growth due to reduced system dynamics, even if nutrient levels are low.”
Public Perception
Local perceptions of aquatic plants vary. In the River Spree area, 80% of residents and 63% of temporary users find native aquatic plants bothersome. Residents are more concerned about the impact on biodiversity compared to recreational users. Conversely, in South Africa’s Hartbeespoort Dam, over 90% of people find non-native water hyacinth intrusive, with concerns mainly about biodiversity.
Effects of Plant Removal
Mechanical removal of aquatic plants is a common management practice. However, this can have mixed results. Removal often leads to a drop in water levels, which can be either beneficial or detrimental depending on the context. For example, in the River Spree, regular mowing has reduced water levels temporarily, but plants quickly regrow.
Moreover, removing plants can increase nutrient concentrations in the water, as plants absorb nutrients and filter particles. When plants are removed, nutrients previously trapped in sediments can be released back into the water.
Control of Non-Native Species
Efforts to control non-native species, like water hyacinth in South Africa, may not always solve the problem. Removing one invasive species can sometimes lead to the proliferation of another, as seen with common salvinia.
Biodiversity Concerns
Aquatic plants contribute significantly to habitat complexity and biodiversity. While some studies show high diversity in macrophyte-dominated lakes, others reveal a decrease in biodiversity due to dense, single-species mats. This can lead to homogenized aquatic communities and negatively impact biodiversity.
Balancing Ecosystem Services
The study underscores the importance of considering ecosystem services in managing aquatic plants. Recreational activities such as fishing and boating often dominate the value assessments, but few users are willing to invest in extensive removal efforts.
In the River Spree, maximum plant removal increased fodder production but decreased biodiversity, particularly in wetland plants. Dr. Hilt concludes, “Management decisions often favor specific user needs. However, our research suggests that the overall societal benefit of removing aquatic plants may not exceed allowing them to grow. The option of ‘doing nothing’ should be considered more seriously.”
Conclusion
The study suggests that aquatic plant management should be approached with careful consideration of both the benefits and drawbacks. In some cases, allowing plants to thrive might offer more overall benefit than continuous removal efforts.