Human impacts and Anthropocene environmental change at Lake Kutubu,a Ramsar wetland in Papua New Guinea

The impacts of human-induced environmental change that characterize the Anthropocene are not felt equally across the globe. In the tropics, the potential for the sudden collapse of ecosystems in response to multiple interacting pressures has been of increasing concern in ecological and conservation research. The tropical ecosystems of Papua New Guinea are areas of diverse rainforest flora and fauna, inhabited by human populations that are equally diverse, both culturally and linguistically. These people and the ecosystems they rely on are being put under increasing pressure from mineral resource extraction, population growth, land clearing, invasive species, and novel pollutants. This study details the last ∼90 y of impacts on ecosystem dynamics in one of the most biologically diverse, yet poorly understood, tropical wetland ecosystems of the region. The lake is listed as a Ramsar wetland of international importance, yet, since initial European contact in the 1930s and the opening of mineral resource extraction facilities in the 1990s, there has been a dramatic increase in deforestation and an influx of people to the area. Using multiproxy paleoenvironmental records from lake sediments, we show how these anthropogenic impacts have transformed Lake Kutubu. The recent collapse of algal communities represents an ecological tipping point that is likely to have ongoing repercussions for this important wetland’s ecosystems. We argue that the incorporation of an adequate historical perspective into models for wetland management and conservation is critical in understanding how to mitigate the impacts of ecological catastrophes such as biodiversity loss.

Wetlands provide a range of benefits to human, animal, and plant life and yet are under increasing threat from industrialization, expanding human populations, and climate change. In 1975, the Ramsar Convention was established to promote the sustainable use of wetlands and halt their decline worldwide (1). One of the commitments that parties to the convention make is to declare as early as possible any changes to the ecological character of Ramsar wetlands as a result of developments, pollution, or other human interference (2). This requires knowledge of the “natural” or “baseline” state of the wetland prior to major human interference (3, 4), as well as ongoing monitoring of the site. In some cases, major alterations to wetlands have occurred prior to Ramsar Convention listing, and so the baseline state is not known. Baseline information can be obtained from a multiproxy analysis of sediment core records that built up prior to the altering event (5). These sediment records can also be used as a cost-effective way to track changes in the ecological health of the site during and after such disturbances (3, 4). Here, we use the case study of Lake Kutubu, a Ramsar site in Papua New Guinea (PNG; Fig. 1), as a demonstration of this approach.Open in a separate windowFig. 1.Sediment cores, resource extraction infrastructure, and settlements at Lake Kutubu, PNG. The green dotted line is the catchment boundary. The shaded areas are 1,000 m contours after Bayly et al. (16). This map was created using ArcGIS software by Esri (http://www.esri.com) and contains information from Humanitarian OpenStreetMap Team Open Street Map (HOTOSM) PNG Waterways (https://data.amerigeoss.org/tl/dataset/hotosm_png_waterways) and PNG roads 2014 (https://png-data.sprep.org/dataset/png-roads/resource/2ea995e6-6483-42db-a71a-ad58f9fbb2de), which is made available under the Open Database License (https://opendatacommons.org/licenses/odbl/1-0/).Paleoenvironmental ecological baselines have been successfully developed to define “limits of acceptable change” for Ramsar wetlands in several countries (e.g., refs. 5, 6). The feasibility, cost-effectiveness, and long-term assessment of these baselines allow for any country, independent of economic status, to assess the impacts of resource extraction, other human activities, and climate change on wetland areas. Baselines have the potential to function as ecological tools for environmental justice and to support local communities in tracking the state of their environment. They can also support the Ramsar Convention by providing evidence for ecological impacts and highlighting areas in need of better management.The Ramsar Convention was adopted in PNG on 16 July 1993, and Lake Kutubu (Ramsar site no. 961) was declared a Ramsar site in 1998 (7), due primarily to its exceptional levels of fish endemism supported by food chains based on unique species of autochthonous primary producers (8). It was determined that significant degradation or loss of the lake would substantially reduce the ecological diversity of the region (8). Yet, at the time of listing, the Lake Kutubu region had already been subject to altered scales of human disturbance with the establishment of European administrative bases in the 1930s (9), low-level development from the 1940s to 1970s, and then the much more significant impacts relating to the establishment of petroleum and natural gas projects from the 1980s (10, 11), followed by large-scale land clearance, construction, and immigration into the area (10, 12, 13). A baseline study of the lake’s condition prior to these disturbances is needed to understand the scale of change and to provide a restoration target (14). Such targets are essential where ongoing development pressures and environmental governance issues can otherwise lead to long-term degradation of environments and livelihoods. We apply a paleoenvironmental multiproxy approach to assess the history of contamination, ecological impacts, and deforestation in sediments of Lake Kutubu. The identification of detrimental impacts in Lake Kutubu is crucial to provide guidance for the implementation of mitigation measures in tropical lakes under similar modern pollution pressures. This approach includes the analysis of fire and pollution indicators, aquatic algae, chlorophyll-a, and geochemistry in the lake sediments from before and after resource extraction activities commenced, providing a detailed profile of chemical and ecological changes. These data are compared to historic records and observations on the state of the lake prior to and since the start of resource extraction in the 1990s.