All change: seasonal transformations in the freshwater hydroscape

The Natural History Museum team has recently returned from our final visit to the beautiful Norfolk countryside, completing the seasonal sampling for our research on disease distribution and concluding the collection of freshwater bryozoans for our project on gene flow and genetic diversity in this region. We teamed up with Stirling University’s Zarah Pattison for an action-packed week of sample collecting.

To briefly recap from one of our earlier blog posts Waders at the ready! Sampling underway in the Norfolk Broads for the Natural History Museum Team, the NHM team is involved in two key research topics of the Hydroscape project. One project entails using molecular approaches to identify the DNA of key disease agents in environmental samples (water and sediments) – the so-called environmental DNA, or eDNA approach. These disease agents include human pathogens (belonging to the Apicomplexa phylum) and fish parasites (Myxozoa and Ichthyosporea) and are described further in a subsequent blog. In our other project we are using highly variable markers (called microsatellites) to characterise gene flow and genetic diversity in populations of two bryozoan species that vary in dispersal capacity and habitats – Cristatella mucedo and Fredericella sultana. We collect overwintering stages (called statoblasts) of C. mucedo from sediments of lakes and ponds and live colonies of F. sultana from rivers and streams. The overall purpose is to investigate how varying levels of connectivity and stressors in the freshwater hydroscape can affect disease distributions, gene flow and genetic diversity.

Images: Alder root on River Glaven from which live colonies of Fredericella sultana were collected (upper left). Tangled colonies of F. sultana attached to alder root (upper right). Close-up of F. sultana to showing branching nature of colonies (lower left). Close up to show feeding tentacles (lophophores, each approx. 0.8 mm in diameter) of F. sultana. Lophophores are used to feed on small particles (algae, bacteria)

Images: Colony of the bryozoan Cristatella mucedo (left) during the growing season (summer) with extended lophophores (each approximately 1mm in diameter). Colony of C. mucedo at end of the growing season – essentially a bag filled with statoblasts (approximately 0.8 mm in diameter) not yet released.


Round statoblast (~0.8 mm in diameter) of Cristatello mucedo present in a sediment sample along with two, saddle-shaped overwintering states (ephippia) of Daphnia

We’ve undertaken intensive seasonal sampling in spring, summer and autumn this year. The latter was completed in early October, when, as during our previous visits, the sun was shining for most of the week! In total we have now collected seasonal samples of water and sediment from 17 sites (Map 1) and freshwater bryozoans from 29 sites (Maps 2 & 3) across Norfolk.

Map 1: Sampling locations (red stars) around Norfolk for seasonal research on disease distribution


Map 2: Sampling locations (pinpoints) around Norfolk for our research on gene flow and genetic diversity in the freshwater bryozoan Cristatella mucedo. Green numbers next to sampling location names indicate the number of C. mucedo statoblasts collected


Map 3: Sampling locations around Norfolk for our research on gene flow and genetic diversity in the freshwater bryozoan Fredericella sultana. Green number next to sampling locations names indicate the number of F. sultana colonies collected


By returning to the same locations over different seasons we can appreciate how much sites can change over such short time frames. Some changes can be restrictive.  For example, access to sites can be greatly reduced by vegetation that has sprung up in as little as two months, and roads previously used to access sites can become ‘rivers’ after a lot of rainfall (as occurred in summer). Such changes in the hydroscape may have interesting implications and are one reason that our research includes sampling the same locations throughout the year. Connectivity and stressors to freshwater systems inherently change with varying environmental and hydrological conditions, and temporal sampling allows us to investigate how the presence of disease agents may change in response to diverse conditions, including more infrequent events such as large storms and flooding.

Blickling Lake in spring where we collected samples for out disease distribution project and statoblasts of Cristatella mucedo


Idyllic summer day on the River Bure where we sampled for the Bryozoan, Fredericella sultana, growing on submerged roots of riparian alders


Seasonal change and unusual events can also affect the condition and composition of the water samples that we collect. For instance, rain can cause runoff to lakes and rivers from surrounding agricultural land which is often laden with fertilisers, thus affecting nutrient load, salinity and oxygen levels in the water. These events may also influence the abundance and distribution of disease agents. Increased runoff, for example, may well lead to an increase in the abundance of Toxoplasma gondii in surface waters. These are the types of questions that we will be asking as part of our research.

Because our research on disease distribution involves filtering large volumes of lake and river water to concentrate the DNA of targeted disease agents (see separate blog post), we can deduce a fair amount about environmental conditions based on the filtration process itself. For example, water bodies with high microalgal biomass can take many hours to filter, since algae cells can block the filter pores, slowing the filtration process. A record for the longest filtration time of a 2 litre water sample was 8 hours and 57 minutes during our July visit! The quickest 2 litre samples can be filtered completely in less than 30 seconds!

Left; filtration apparatus for the filtering and concentration of DNA from water samples under a vacuum pump system. Right; polycarbonate filters used to collect the DNA from filtered water samples


An added benefit of working in the great outdoors is the delightful array of Great British wildlife that may be encountered and observing how the countryside changes over the year – for example discovering the one of the most amazing bluebell wood any of us has ever seen!

Bluebell wood in full bloom during our spring visit to Norfolk


Our wonderful wildlife spotting opportunities included observing local inhabitants such as adders, grass snakes, kingfishers, cuckoos, marsh harriers, huge evening flocks of starlings going to night-time roosts, many species of wildfowl, and bats. We even made a few friends along the way in the form of curious sheep, inquisitive swans and some very social alpacas! In October we observed overwintering wildfowl, including pink-footed geese and whooping swan. Some of the sites we visited are so important for migrating and overwintering birds that they are protected under UK legislation as Sites of Special Scientific Interest (SSSI’s).

Overwintering pink-footed geese flying away from Wolterton Lake, North Norfolk, to nearby pasture for foraging


With the 2016 fieldwork completed, we are excitedly planning next year’s work. During 2017 we will conduct seasonal sampling at the two remaining focal landscapes identified in the Hydroscape programme – Greater Glasgow and Cumbria.

In the meantime, we’ll be busy working away in the lab processing the hundreds of samples that we have collected over this past year. So, better get to it!


NHM Team





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