FLOATLANDS AS ECOLOGICAL TOOLS BALANCING PROMISE WITH REALITY

UNDERSTANDING FLOATLANDS IN AMSTERDAM: EVALUATING ECOLOGICAL IMPACTS, DEVELOPING AN ASSESSMENT FRAMEWORK FOR FLOATLANDS TO CONCEPTUALIZE DESIGN PRINCIPLES FOR ECOLOGICALLY SENSITIVE FLOATLANDS

Problem Statement
Ecological water quality in the Netherlands is critically poor, with only 17% of water bodies meeting the EU’s required standards. Climate change exacerbates this issue, increasing the risk of algal blooms, oxygen depletion, and biodiversity loss. Floatlands are proposed as a potential solution to improve ecological water quality by providing ecological benefits such as water filtration and habitat enhancement. However, their ecological performance is underexplored. This study investigates their impact on ecological water quality, focusing on both biological and chemical indicators.

Theoretical Background
This study draws on the DPSIR framework to evaluate how floatlands impact urban water quality by balancing benefits (e.g., nutrient filtration, habitat creation) and risks (e.g., shading, oxygen depletion). The impact of floatlands depends on the ecological state of the water body with context-specific factors like water quality, depth, and shoreline conditions, highlighting the need for tailored approaches to their design. These insights guide the development of an assessment framework to systematically evaluate their role in improving or degrading urban aquatic ecosystems.

Methods
A mixed-method approach was applied to evaluate the ecological impact of floatlands. Qualitative methods, including literature review and expert interviews, identified key ecological metrics for assessing floatlands’ effects. Quantitative fieldwork at Boerenwetering and Kattenburgerskade measured biological (macrofauna, vegetation) and chemical (pH, dissolved oxygen, temperature) indicators to compare floatland areas with open water. The results informed an assessment framework linking water body ecological state of the sample locations to floatland impacts. The insights lead to the conceptualization of design principles for ecologically sensitive floatlands.

Main Findings
The impact of floatlands on ecological water quality varies across sites, emphasizing the importance of local ecological states. Floatlands had minimal influence on chemical water quality (e.g., pH, dissolved oxygen, and conductivity), with no statistically significant differences observed between floatland sites and open water. However, biological metrics, particularly macrofauna presence, revealed their potential ecological contributions.

At Boerenwetering, the impact of floatlands on ecological quality was high (score: 3.6), which was reflected in the site’s relatively higher ecological state (score: 3.2). The positive impact was attributed to favourable conditions such as naturalized shorelines and boat-driven water flow, which mitigated wave action and enhanced habitat quality for macrofauna and underwater plants. In contrast, at Kattenburgerskade, floatlands had a lower ecological impact (score: 2.6), which corresponded with the site’s poor ecological state (score: 2.3). Stagnant, turbid water and excessive shading reduced the benefits of floatlands, worsening light conditions and limiting plant growth and habitat quality. Similarly, Marineterrein showed a moderate impact (score: 2.6) due to steep, modified shorelines and insufficient light, reflecting some of the site’s constraints on floatland effectiveness.

The assessment framework effectively evaluated floatland contributions through metrics like light climate, habitat suitability, and plant contribution scores. Boerenwetering’s plant contribution score (3.9) outperformed Kattenburgerskade’s (3.1), underscoring the influence of plant selection and ecological context on floatland performance.

Conclusions and Discussion
Floatlands can enhance biodiversity in favourable conditions, particularly by supporting macrofauna and improving habitat complexity. However, they have minimal effects on chemical water quality. The success of floatlands depends on local ecological conditions, as demonstrated at Boerenwetering and Kattenburgerskade. The assessment framework shows promise as a tool for evaluating floatland designs but needs refinement for broader application.

The developed assessment framework shows promise as a practical tool for evaluating and guiding floatland design. It effectively considers ecological states and floatland features, though it requires further refinement for broader application. Future research should focus on optimizing floatland designs for diverse environments and improving their ecological contributions.

Recommendation
To enhance floatland effectiveness, three design principles are key: maximizing sunlight access, incorporating vertical structures to increase habitat complexity, and selecting native plant species with dense root systems. For Marineterrein, further research is needed, especially as the floatlands will cover a larger area, potentially altering water chemistry. The findings from Boerenwetering and Kattenburgerskade provide valuable references for optimizing floatland designs.

By incorporating these design principles, floatlands can improve urban water quality and foster healthier aquatic ecosystems.