Frampton Marsh - North Scrape diggings. What we're doing and why.

Have rediscovered this blog that I wrote and didn't post after the work we did two winters ago. Have now tweaked it t be relevant to the work we're now doing on North Scrape. I will give you a basic breakdown of how scrapes are managed and why it's so important to do this work.

Scrapes – Water management

This is the most complex and technical part of the current work and ongoing managment, so please bear with my explanation. We often get asked, and far too frequently told, about our water levels. Mostly visitors want to know why and I don't mind explaining at all, occasionally though we do get told our water levels are either too high or too low and that does niggle. We haven't won the Golden Welly for being the best reserve for waders three years (and hopefully a fourth this year) by fluke and coincidence. Having a lot of water or an absence of water at certain times of year isn't key to managing a good reserve, what you do with the water you have is the most important thing and always keeping an eye on the next few months. 

Rant over (sorry), now for some technical stuff....

Many reserves that have scrapes or pools which don’t have the option of good water level control will, and rightly so, cover their backs and have high areas to provide a refuge in case of floods and lower areas that stay wet in case of dry spells. While sound in principle this increases the gradient of the land, potentially reducing management options and suitable feeding habitats for a variety of species throughout the year, particularly passage waders, a Frampton speciality.

A diagram may be an easier way to understand....

Fig 1. Example of a deep scrape

This illustrates a scrape with high islands and deep pools. Islands can’t be flooded to control vegetation in the winter, there is little feeding area for passage waders, and during the summer food sources in the deeper areas are inaccessible for parents feeding chicks and newly fledged young. While an extreme example, this is the problem we had in north and middle scrape. We were unable to flood the tops of islands to kill off vegetation over the winter and our sluices weren’t in the right places to draw the levels right down, exposing as much feeding mud as possible at the end of summer.

In this example the scrape ground levels have a range of 1.8m so a 30cm draw down gives a relative surface feeding area of 3.6 (this is purely an illustrative figure and means absolutely nothing).

Fig 2. Example of a shallow scrape

A shallow scrape allows more to be done with less water. We can flood the islands easily to suppress vegetation prior to the breeding season and with correct placement of sluices we can drain all the water off. Also smaller variances in the water levels provide much more habitat for feeding waders.

Compared to the deep scrape our new and improved shallow scrape has a 0.7m range in levels so the same 30cm draw down provides an increase of over 75% in relative surface feeding area. 

So this is what we're doing on North Scrape, reducing the gradient by taking spoil from the high areas and raising the lower areas. This is by no means complete and we will have another crack at it next year. 

Scrapes – Islands

We have had a play with our islands. Tweaking their shapes and sizes, heights and relative depths around the perimeter. With monitoring over the coming years we will be able to identify criteria to make the perfect island. This will not only benefit further work at Frampton and Freiston but also at RSPB reserves with similar habitats around the country.

By varying the height of these islands we can expose them at different times throughout the year, allowing for late arrivals or failed breeders. If all the islands were the same height and available at the same time then resident breeders (ie Black-headed Gulls and geese) would dominate and out compete migrant breeders (terns and waders).

Scrapes – Ecology

So why is water level management so important? Well it all depends on what’s in the mud and what’s in the water.

Benthic invertebrates live in the mud and we want as many of these organisms as possible, specifically we want the larvae of chironimids, also known as non-biting midges. These are the flying insects that make up the swarming clouds that you can see around the reserve from warm February days onwards. Their larvae are called bloodworms because of the high levels of haemoglobin, allowing them to absorb oxygen to survive in the gas depleted mud. They are super tasty and waders love them so for us to be a wader magnet of a reserve we have to become a bloodworm farm.

Referring back to my first sentence, we are going to do this in two ways. Increase nutrients in the mud for the larvae to feed on and reduce nektonic (free swimming) invertebrates in the water that compete with waders by preying on bloodworms.

We are looking to increase nutrients by sowing crops in the mid levels (green lines in Fig 2) of the scrapes. These crops will be seed rich and water intolerant, allowing us to flood them in late Autumn which will lift their seeds to the surface for wildfowl to feed on and kill of the green matter which will rot down to provide food for our bloodworms.

Nektonic invertebrates will be removed from the scrape’s ecosystem during the sowing year by drying the scrape out entirely in that year. By mid May we want 80% of the scrape to be dry, which will provide small pools full of nektonic and benthic inverts. We will put no water on during the summer so by August the scrape should be completely dry, with all free swimming inverts removed. Re-wetting will kill the crop and provide a food source for bloodworms which, with no nektonic predators, will flourish. This abundance of food will draw in a variety and number of waders. Over 3-4 years, nektonic species will re-colonise the scrape and compete with the waders for the bloodworm bounty. Benthic biomass will en start to decrease and along with it the wader numbers. This is the time we drain down the scrape and start the process all over again. The three scrapes and 2 hide layout at Frampton will allow visitors the opportunity to see this process in action while at the same time having a ‘normal’ scrape to enjoy.

We have had two years of scrape cropping now and will try and find some time to write that up for you all as well.

That is a very quick background to what's happening here and why. We are getting asked about it a lot, which is great that our visitors take an interest, so hopefully this blog is of interest too (and give you something to read while I find time to do the sightings blog). If you have any questions or queries, please ask away or catch me on the reserve. 

T