Kwaheri Mara!

It's always bittersweet leaving the Mara. This place is our second home, and we have a beautiful camp, good friends and an amazing river we hate to leave behind. On the other hand, after several months of no running water, limited solar power, and the same 4 outfits, you do start to long for modern conveniences. I usually crave salad, hot showers, a nice cappuccino, and a leisurely morning spent on my computer with the screen at full brightness. Nevertheless, the time has come to return to the US-- we have a lot of samples to analyze in the lab, lots of papers to work on writing, and Chris is a teaching assistant for a class this semester. It's going to be an exciting year... We'll be working with Ella and James to write up their senior research projects. Chris and I both have several papers we're working on publishing from our research. And we have a super exciting field season we're planning for 2017! Already excited to think about heading back here.... Until then, kwaheri Mara (goodbye)!

Hippos on the bank of the Mara River

Our home in the Mara

Why we need wiper blades on our sensors

It's really important for our research to be able to measure water quality in the river on a continual basis over long periods of time. To do this, we have some pretty amazing water quality sensors made by Eureka, that can measure lots of different water quality variables and store the data for weeks or months at a time. We have had these sondes for 6 years, and we have put them into some of the most challenging conditions I can imagine, and they just keep plugging along. Our model has the extra benefit of a wiper blade that cleans the surface of each sensor just before taking a new measurement, which is critical in the Mara for preventing biofilm or dirt from fouling the sensor and compromising the measurement. However, we still have to pull the sonde out of the river every few weeks just to clean off all the bugs, hippo poop and biofilm that accumulates.

Our water quality sonde after 3 weeks in the river

Where is all the algae going?

Hippos and wildebeest load a lot of nutrients into the Mara River... like, a lot. All of those nutrients should fertilize the river and produce a lot of algae. It's what the textbooks say should happen, and it's what research in other rivers show should happen. We see it happen in some portions of the river where there are only moderate levels of hippo inputs. However, it is not what happens where the hippo and wildebeest inputs are highest. Why not? I don't know. 

This-- getting results that don't fit your expectations, that surprise you-- is simultaneously the most exciting and the most frustrating part of science. It's the part that makes science addictive, that keeps you coming back for more, that makes you think grand discovery is on your doorstep. It's also the part that can drive you crazy and make it difficult to publish your research. If you're getting an unexpected result, you need to 1) be absolutely sure it's a real result and not an artifact of something you screwed up on accident, and 2) figure out why you're getting it. "This is weird, and I don't know why it's happening," will only get you so far. 

So, back to our algae... Why don't we see more in the river? Is it not growing in the first place? Or is it growing and going somewhere? I have been asking this question a lot over the last year as I have been working on the final papers from my dissertation, and this summer I was able to run a pilot experiment to test what is becoming my primary hypothesis... hippo and wildebeest inputs provide so much food for bugs and fish that their populations increase and they then graze down the algae. This would be really cool if it turns out to be true, because it would show that animal inputs can enter the river food web through various pathways, and which pathway they follow determines how those inputs shape the river ecosystem. Or I could be wrong and it could be something else entirely... See? Exciting, and a little frustrating. 

So, to test this hypothesis, I set out a grazing exclusion experiment this summer. I basically grew algae in the river on glass discs (the white circles in the picture below). Some discs were protected from grazing (either by a cage to restrict fish or by insecticide to restrict bugs) and others were not. If there was more algae growing on the protected discs than on the not-protected discs, that would suggest that algae can grow in the river, but it doesn't accumulate there because it gets grazed down. 

Before deployment in the river

I wasn't originally planning to run this experiment this year, as we already had a full schedule, but I was excited to be able to put this together almost completely with supplies we had stored around our camp. I built two of these that I deployed at two different sites in the river. I left them out for two weeks and hoped they didn't get stepped on by a hippo, washed away in a flood or collected by an enterprising Maasai person with a need for some glass discs. I always consider it a major win when we put something out in the river and return later to find it still there. 

After 2 weeks in the river

After two weeks, we collected the glass discs and measured the chlorophyll on them as an indication of how much algae was growing there. To my excitement, the discs protected from grazing by insects had more algae than the discs that weren't protected, supporting my hypothesis! To my frustration, the cages protecting the discs from fish caught a lot of hippo feces which influenced those data, and the variability was so high that my insect results weren't statistically significant. Ah science... the perfect career for those who love a good challenge! So, I can't say I've solved this mystery yet, but I'm getting closer, and I'm already excited about getting back to the field next year to try again. 

Sundowner farewell

One of the great traditions in East Africa is the sundowner, where you head out into the savanna, armed with a box of wine or a cold Tusker and some cheese and crackers if you're lucky, and watch the sunset. It's hard to describe the splendor of this moment, with the grassland turning golden in the last moments of light; the streaks of red, purple and gold reflecting across the wide open sky; the silhouette of elephants in the distance. It seemed the perfect way to send Ella off after a great and successful summer of field research. Kwaheri Ella and thanks for a wonderful summer!

Ella watching the sunset from the roof of the Land Rover

Testing hypotheses in artificial streams

Ella has been able to collect detailed data on gas emissions from 13 hippo pools, in addition to the 12 hippo pools we sampled last year. This will give her a nice range of hippo density and river flow level in order to test how these two factors influence gas emission levels. However, all the variability often present in the field can often make it difficult to accurately determine the influence of various factors, so Ella designed an experiment in the artificial streams to test her hypotheses more directly.

She added blackwater from the bottom of a very concentrated hippo pool to the artificial streams in varying concentrations.

Ella adding black water to the artificial streams

Then she ran the streams at different velocities.

Ella's artificial stream experiment

At various time points, she collected water samples from each stream and collected dissolved gases from each sample into vials which will be analyzed back at the Cary Institute. Actually, we had a team of 4 people working as fast as possible every 45 minutes throughout a whole day to collect the water samples at specific times. Again, we were lucky to have a great team!

Ella collecting a gas sample

We couldn't analyze any of the gas data in the field, so we won't know the results of this experiment until the fall, but all of the dissolved oxygen data from the streams suggest we were successful in capturing the range of conditions we were hoping for. Can't wait to see how all of this comes together!

Greenhouse gases from hippo pools

Over the last few weeks, Ella has been collecting water samples from a lot of different hippo pools in order to measure how hippo pools may contribute to the emission of greenhouse gases. Hippos load a lot of carbon into pools through feces, and as that feces decomposes, it uses up the oxygen in the water and the decomposition process emits greenhouse gases like carbon dioxide and methane. Ella is studying how the number of hippos and flow of the river influence the quantity of greenhouse gases being emitted. 

To collect these data, Ella has had to collect water samples from a lot of different hippo pools, which can be a... let's say... exciting adventure. Hippos are the most dangerous animal in Africa, and it is particularly dangerous to get between them and the river. The easiest way to access a hippo pool in the Mara is to follow a hippo trail down to the river's edge, and crouch there while you fill your sample bottle, keeping an active lookout for hippos and crocodiles. We always hire an armed ranger and spend a lot of time scouting a hippo pool before we collect samples there, and we always make conservative decisions about which pools we feel we can sample safely, but it is still an activity that really makes you feel alive. Ella handled it like a complete pro!

Ella collecting a water sample from a hippo pool

Much of the sample processing needs to be done as soon as possible, so we take a mobile lab in our Land Rover and do a lot of chemistry in the field. However, some samples need to be analyzed later in our lab tent (affectionately called the Lady Cave, because of all the hours I have spent doing chemistry in there, it's small cave-like interior, and the tendency of bats to roost in and around it). Here's Ella busting out some serious field chemistry in the Lady Cave, late into the evening, equipped with a head lamp to see the readings. Epic!

Late night chemistry in the lady cave

Low cost sensor course in Tanzania

In August, Chris taught a course on low-cost sensor technology for the Tanzania water resource management authorities. This course was part of SELVA - the Serengeti Lake Victoria Sustainable Water Initiative for the Mara River - which is run by our friend and colleague Beth Anderson at FIU. Chris taught the course participants how to build low-cost water depth and water quality sensors using the open-source Arduino platform, and then the team was going to deploy various loggers at sites throughout the basin. This technology is so powerful, especially in places like East Africa, because it allows people on the ground to build and maintain their own sensors, rather than relying on expensive "black box" instruments that have to be shipped off for repair at great expense. Chris has already done some really great work training people in Arduino sensors in the Kenyan portion of the Mara Basin as part of MaMaSe - the Mau Mara Serengeti Sustainable Water Initiative - and this is an exciting new extension of that project. Ella was interested in learning about low-cost sensor development, so she attended the course.

Ella at Lake Victoria

For me, this meant a lovely week off hanging out with Lily in the charming lake-side town of Musoma. I love this town! It's right on the shores of Lake Victoria, so there are beautiful beaches, delicious fish, and a laidback beach town vibe. Musoma is located very close to the Mara Wetland, where the Mara River flows into Lake Victoria, so we have visited here a number of times. We currently have an ongoing project with WWF analyzing sediment cores in the Mara Wetland, so it was a great opportunity to visit the wetland as well and check in with our colleagues.

Beach on Lake Victoria

Musoma is also an amazing place to shop for kitenges, the brightly colored and boldly patterned African fabrics that many women wear. I love shopping for kitenges, and I was excited to get Ella into it. We couldn't resist having a few outfits made for us in the market.

Ella visiting with a seamstress in the market

Can we make a hippo pool in a bottle?

This summer Chris set up one of the big experiments for his dissertation. He is interested in studying the influence of the microbial community on biogeochemical cycling in the bottom of a hippo pool, and the interacting effects of carbon loading and microbial community structure on those effects. He came up with a really clever way to test this by developing small "hippo pools" in 1 liter bottles, which allowed him to have lots of replication across different treatments. In total, he set up around 150 bottles!

Chris weighing hippo poop into a bottle

We sampled the bottles for about 12 different parameters at various time points over a few weeks. We could see some of the results immediately in the field as we collected the data, and it was really exciting to watch the changes in the different treatments over time. A lot of additional data will be analyzed from this experiment back in the lab at Yale. 

The team at work

It was a ton of work, but the preliminary results are really interesting. We saw some of the changes we expected to see, and others that were a complete surprise. Unexpected results are often the most exciting in science because they suggest new hypotheses and mechanisms you may not have considered already. We also had a great team, which makes all the difference. Everyone had a job, James played DJ on his ipod, and we had a lot of fun!

Team Hippo Pool