The Meaning of “Natural”: Otmoor RSPB Reserve

By Medha Mukherjee, WSPM ’20-21

Photo by William O’Sullivan, WSPM ’20-21

As the global population continues to cope with the COVID-19 pandemic, a team of Water Science, Policy and Management (WSPM) students, embarked on an induction field trip to the Otmoor RSPB (Royal Society for the Protection of Birds) Reserve on a cold October morning. They were ready to wade through the wetlands in small groups, keeping their face masks on and walking two meters apart but grateful to experience something in person months into the new Covid reality of 2020. The objective was to understand the historical background of the wetlands to be able to critically engage with its current contexts of maintaining water quality, managing water levels along with natural flood management, which are in place to meet the RSPB’s aim of nurturing certain bird species. But all through the trip led by their Course Director Dr. Jocelyne Hughes, Dr. Troy Stenberg and Patrick Thomson, one vital question kept coming to the surface – What does “natural” really mean in a highly manipulated freshwater ecosystem?

Located to the northeast of Oxford, Otmoor is a low-lying area of roughly 1000 hectares, the social history of which relates directly to its current hydrological and environmental issues. Once a marshland, with the River Ray as its primary source of water, Otmoor was drained after the 1815 Act of Enclosure, and the River Ray rechanneled, in an attempt to turn the wetland into a farmland. The move had disastrous effects, causing severe downstream floods with the villagers rioting and breaking the embankments to let Otmoor flood naturally again. Then in 1997, the RSPB established the nature reserve, isolating the wetland from the river system. It is now a precipitation-based wetland, with a strong water balancing system in place for the creation of a conducive habitat for bird species such as snipe, redshank, lapwing and others, in a rather expensive attempt to control the ecosystem. The water levels are maintained with the help of pump stations up and down the reserve, with trenches cutting through the grasslands, and scrapes and surface ponds dug out to hold water. To further conserve biodiversity, cows are used to graze out dominant plant species and increase biodiversity, and electric fences keep predators such as foxes and badgers out, thus ensuring a safe nesting ground for the birds. One student commented how surprised he had been that a seemingly pristine wetland was actually sustained with hidden pipes and pumps.

The WSPM team was joined by Heather Bond, an Oxford WSPM alumna currently working for the Environmental Agency, who further explained the hard engineering approaches for natural flood risk management and the efforts to create an optimal balance between letting the wetlands flood naturally, and keeping the rising water levels from affecting nearby farmlands and villagers. As the students stood on a bund constructed for flood risk mitigation, they looked out onto the vast green stretch of serene wetlands under the pouring grey sky, realizing how the sheer magnificence of this “natural” habitat is actually held in place and carefully managed by a highly mechanized system. Thinking about the meaning of “natural” in the age of the Anthropocene, thus, becomes a moral imperative in environmental and socio-political enquiry.

Owing to increasing rainfall, the field trip finally ended in a barn with a deeply insightful session conducted by two local female farmers who manage an award-winning flock of sheep at the nearby Hill End Farm in Noke. They shared first-hand experiences of living in a wetland area, tackling the binary of either being too wet or too dry—the need for a very delicate balance to maintain equilibrium for natural wildlife and the sheep–while dealing with water pollution from raw sewage discharge, which is poorly managed by a private utility company.

Two days later, Hill End Farm messaged the group about the weekend of rain, “I had to evacuate the ewes out of the lower field yesterday morning. I recorded 50mm in 24 hours…It does seem weather patterns are changing.” In some locations 50mm in a day would be high but not unusual. In Oxfordshire, that amount marked the highest amount of rainfall in 24 hours since observations began in 1827. On this field trip, students had seen first-hand humans have manipulated the environment at Otmoor to ensure co-existence between wildlife and humans, but can that balance be maintained by anthropogenic activities when it comes up against the looming extremes of water in the climate change crisis, also propelled by anthropogenic activities?


Aerosol Effects on Precipitation and the Hydrological Cycle-A Discussion

A wide range of aerosol effects on precipitation and the global hydrological cycle have been proposed. These can be broadly categorised into radiatively and cloud-microphysically mediated effects. Aerosol effects on precipitation have traditionally been assessed bottom-up, modelling or observing the processes involved from aerosol emissions via microphysical processes all the way to precipitation formation. However, such assessments rely on a complete understanding of a very complex and uncertain process chain and have been shown to be subject to large uncertainties.

In this presentation, Prof. Philip Stier will provide a comprehensive overview of aerosol effects on precipitation, summarising the findings of a number of recent expert workshops. He will also show that the response of regional precipitation to idealised and realistic aerosol radiative perturbations can be constrained top-down through an energy and water balance framework because associated changes in the net diabatic heating / water transport need to be balanced by latent heat release, surface or top-of-atmosphere fluxes or compensated for by energy / water divergence.

However, this physical perspective of aerosol effects on precipitation has its limitations and provides no answers to key questions about their impact: which kind of precipitation changes have the biggest impact for mankind and ecosystems? Which regions of the globe are most vulnerable? What aspects of precipitation changes (in terms of changes of its intensity distribution and location) should we concentrate on? Are there objective ways to answer these questions? Please come ready to discuss these questions and more!

*Please note that registration for this event will close 3 hours before the event takes place. You must be registered to participate.

About the Speaker

Philip Stier is a Professor of Atmospheric Physics and Head of Atmospheric, Oceanic and Planetary Physics in the Department of Physics and a Fellow of the new Reuben College. His research addresses physical climate processes in the context of anthropogenic perturbations to the earth system as the underlying cause of climate change and air pollution. Focal points of his research are aerosol and cloud physics, their interactions and their role in the climate system. He also heads the Climate Processes Group and serve on the steering group of the Oxford Climate Research Network.