According to our global analysis of plastic pollution in freshwater lakes and reservoirs, the level of microplastic pollution in New Zealand lakes is comparable to that in the US or Europe, despite lower population densities. This suggests that two types of lakes are particularly vulnerable to plastic contamination: those in densely populated and urbanized areas, and large lakes with long water retention times. Surprisingly, some lakes in New Zealand have higher concentrations of plastic fragments than the so-called “garbage patches” in the ocean.
In our study, Rotorua Lake in New Zealand had the highest microplastic pollution among the three lakes included in the analysis. This level of pollution is on par with lakes in the northern hemisphere that have much larger populations living along their shores. It is disheartening to find such high levels of plastic pollution in New Zealand lakes, especially considering the country’s green image and emphasis on environmental ethics and stewardship.
Our study is the first to develop a standardized protocol for measuring microplastics in lakes under various environmental conditions. This allows us to compare lakes, quantify pollution, and extrapolate results to other systems. We found that lakes in or near built-up areas had significantly higher levels of pollution compared to less populated areas. However, no lake in the study was unaffected by plastic pollution, regardless of its distance from human activity.
To mitigate the environmental degradation caused by the disposal of products with short life cycles, we need to increase our awareness of their effects.
Lakes as sinks for pollution
We conducted our analysis using data collected by the global lake ecological observatory network (GLEON) from 38 lakes across 23 countries and six continents. While there is extensive research on microplastic pollution in the ocean, there are limited studies on freshwater ecosystems. However, most lakes serve as long-term sinks for contaminants and pollutants, including microplastics. Our analysis focused on measuring small plastic particles ranging from microplastics to macroplastics.
We primarily found fragments and fibers of plastics that are generally easy to recycle, not the hard-to-recycle plastics that are being phased out in New Zealand. This raises questions about how these easily recyclable plastics persist in the environment and enter lakes. The issue of plastic debris in lakes remains understudied in New Zealand.
Ecological impacts
We collected and filtered large volumes of water to obtain representative samples from each lake. Our analysis revealed that smaller plastic fragments, which were dominant in the samples, are small enough to be ingested by various organisms, especially fish and filter feeders like freshwater mussels. This raises concerns about the underestimated effects of plastics on the food web, considering the diverse native and introduced fish and mussels residing in New Zealand lakes. Additionally, plastic pollution in lakes can impact sources of drinking water, with growing evidence of chemical leaching from plastics into water.
This study serves as an early warning and highlights the urgent need for a nationwide baseline survey in New Zealand to assess the extent of plastic pollution in lakes. By identifying sources and hotspots of microplastics, we can inform management strategies to reduce pollution levels.
