On Healing Sick Ecosystems

I am a person who is fascinated by organisms of all kinds. I like the cute fuzzy ones that most people like, but also the scaly, leafy, prickly, stinky, or slimy ones, as well as the ones we can’t see without a microscope but that have outsized effects on the world around them. I am amazed by how many different ways there are to be alive on this planet, and moved by the intricate connections living things have with each other and their environments.

As I began to study the diversity of life, I noticed a pattern: many creatures are in danger because we humans are unintentionally destroying their homes. Whether by pollution, climate change, or clearing habitats to build things of our own, we have made much of the world less habitable for the living things with which we share it. We have already driven some species extinct, and many others are perilously close.

I believe there is a compelling moral case for preserving healthy, diverse ecosystems. There is also a strong practical case: we depend on intact ecosystems for services like clean water, fresh air, and pollinators that help our crop plants reproduce. Living near green spaces also improves our health and society as a whole. Thus, I chose a career studying how to help ecosystems best recover from our more destructive impacts. In my PhD research in Prof. Brenda Casper’s lab at the University of Pennsylvania, I studied how interactions between plants, soil-dwelling microbes, and heavy metals can affect the long-term development of ecosystems on metal contaminated soils.

Pollution and remediation: one site’s story

I conducted my studies in the portion of the Palmerton Zinc Superfund Site owned and managed by the Lehigh Gap Nature Center. The site consists of over 2000 acres on the side of a mountain in upstate Pennsylvania that was devastated by heavy metal pollution from two zinc smelters operating for much of the 20th century. When the site was at its worst, local residents and passersby on the Appalachian Trail, which traverses the site, frequently compared it to the surface of the moon, or the aftermath of a bomb explosion.

The site badly needed some kind of remediation to remove or contain the pollutants and mitigate their threat to human and environmental health. It was (and still is) crucial that remediation be guided by our best scientific understanding of site histories and the effects of heavy metals on humans and the environment. Interference in the form of censoring data about such sites, or letting corporate or political priorities dominate discussions about environmental stewardship, can only make remediation longer and more difficult.

Today, after over a decade of intensive remediation work involving scientists, community members, and numerous federal, state, and private organizations, the mountainside would be unrecognizable from the moonscape described above. Grass species with low metal uptake were planted to build healthy soil while keeping the metals sequestered underground. These grasses, now taller than most people, tower and sway in the breeze. In many places shrubs and small trees are coming in, and in the patches of forest that survived the pollution, dense canopies create cool shade over lush carpets of ferns. Birds, grasshoppers, and butterflies are diverse and abundant, and it is not uncommon to encounter deer at dawn or dusk. Hundreds of hikers and thousands of schoolchildren visit the area each year, largely thanks to land management and educational offerings by the Lehigh Gap Nature Center, which now owns about a third of the site.

Sustained collaboration between scientists, land managers, and community members has been essential to this remediation effort. Early in the process, researchers made valuable contributions by documenting effects of the polluted soils on the site’s plants, animals, and microbes and by testing numerous revegetation strategies. Remediation of a polluted site had not been attempted on such a large scale before, and this early testing was key to the successful establishment of large-scale plantings.

Continuing challenges

Remediation of disturbed landscapes is an ongoing task, and both basic and applied scientific research are crucial to understanding how to do this task well.  Many fundamental questions remained when I began working in the site. For instance, we knew that a group of soil dwelling fungi called arbuscular mycorrhizal fungi (AMF; soil dwelling fungi that trade plants nutrients for sugars) were important for the growth of many plants there, but we had little idea how AMF might affect plant metal uptake or metal tolerance under field conditions. After a couple years of work at the site, in the lab, and on the computer, I found that mycorrhizal fungi have little effect plant metal uptake, but that there is a remarkably close relationship between a plant’s species identity and the chemistry of the soil underneath it. This suggests that once plants are growing in an area, adding AMF will have little effect on their metal uptake. However, knowing what plants are growing in a certain patch of soil can tell us a lot about that soil’s chemistry.

The researchers and managers of the Palmerton site also feared that an uninvited tree species, gray birch, accumulated such high leaf metal concentrations that its leaf litter would elevate metals at the soil surface and poison neighboring plants, including the grasses they had worked so hard to establish. This pollution of soil via leaf litter has been hypothesized to occur but it has not yet been thoroughly tested, and the Palmerton site seemed like an ideal setting for such a test. Again, I investigated, and after a couple years of study, including planting, monitoring, harvesting, and analyzing nearly 500 oak and maple seedlings in the site, my colleagues and I found that metal-contaminated birch leaf litter does not increase surface soil contamination or poison other plants, but that soils under the birches and grasses differ in their concentrations of metals and organic matter in ways that could shape the continued trajectory of plant community development in the site.

How lessons learned from remediation help us rebuild ecosystems better

These findings are already shaping the course of continued remediation and broadening our more general understanding of how metal polluted ecosystems work. We now know that efforts to control plant metal uptake may be better served by altering soils or plant communities directly than by manipulating AMF. We also know that gray birch does not threaten remediation as was feared, though concerns remain that it may shade out the desired grasses or introduce metals into the food chain via its leaves. Furthermore, thanks to the work of dozens of other scientists in this and other contaminated sites, we are learning important information about the continued legacies of pollution, such as how metals do and do not move in groundwater, and the effects of contaminated sites on migrating birds that rest and feed there.

It is clear that conserving healthy, intact ecosystems remains preferable to disturbing them and then trying to rebuild them. As with most diseases, prevention remains far easier and cheaper than cure. However, for those landscapes we have already damaged, science is providing local residents and land managers with tools to improve their lives – and those of their invaluable fuzzy, leafy, or slimy neighbors—by reclaiming and restoring healthy ecosystems.