Pros and Cons of Hydroelectric

Hydroelectric power generates the most electricity of all renewable energy sources in the US, about
7% of the total production. It is a truly renewable source as the same water can flow through a series of dams on a single river, and it is renewable. It is also “clean”, producing no carbon emissions outside of those during the dam building process. 

Water held back by a dam goes through an intake pipe and turns turbines as it passes through the dam.
Faster flowing water will produce more power. Hydroelectric power is about 90% efficient, making it a
great source of power. Due to controls at the dam, the flow of water can be adjusted to meet peak
demands much more quickly than at a nuclear or coal-fired plant. Some dams are equipped with a
pump and can pump water to a higher level during times of low energy usage. The water is then
released back through the dam at peak times to generate additional power.

Not all dams are generating stations, but hydroelectric dams often serve other purposes such as flood
control, irrigation, drinking water supply, and recreation. Because the water is naturally occurring and
free, hydroelectric power is among the cheapest on the market, less than a penny per kilowatt hour on
average. An electric utility can earn additional income through recreational fees, keeping utility rates
low.

Hydroelectric dam in Arizona (USGS)

Although hydroelectric power is “clean”, it is not completely “green”. Like the fossil fuels, it also has
negative environmental impacts. Dams affect fish migration, hydrology, and sediment and nutrient
movement. Flooding a reservoir also causes terrestrial habitat loss, which is traded for aquatic habitat.

Fish ladders can be built to aid anadromous fish in passing around a dam. These fish hatch in
freshwater, live as adults at sea, and return to their native streams to spawn. The journey through
natural aquatic habit frequently involves jumping over small waterfalls, which fish ladders mimic.
Different species of fish move at different speeds and therefore have different needs. Fish ladders come
in many different designs, and some even look like a natural stream rather than a flooded staircase.
Intake screens covering the intake pipes can successfully keep most fish from getting sucked into the
turbines, which can kill them.

Fish ladder (Army Corps of Engineers)

Terrestrial habitat is lost at the expense of aquatic habitat gain. However, the reservoir behind the dam
is of lower quality than a natural lake and alters downstream hydrology. Reservoir water stagnates
since there is no outlet and sediments and nutrients from upstream collect behind the dam rather than
enriching downstream areas. Downstream ecosystems can also suffer if not enough water is released
from the dam.

Sediment deposits after a dam removal in Washington (NPS)

This week's information comes from US Bureau of Reclamation, Michigan DNR, and
Union of Concerned Scientists.

Everglades Ecosystems

This week and next we’re taking a look at the largest subtropical wilderness in America, the Everglades. What we now know as Everglades National Park is just a fraction of the original Everglades, and unfortunately, almost daily it becomes a larger percentage of what of remains today. While what remains is an incredibly diverse variety of habitats, each with their own plants and animals, it is not without its challenges. We’ll explore what’s so special about this place as well as what’s going wrong there.

In its former glory, the Everglades was a huge watershed. Water flowed south from areas north of Lake Okeechobee and drained to the east, west, and south. Some of the water flowed east and west into the Atlantic Ocean and Gulf of Mexico, respectively, through traditional rivers and streams. Some water flowed out through the slow-moving “River of Grass”, as the Everglades became known as. Where the water goes and how much gets there determines the many different ecosystems.

Many other factors go into building an ecosystem, including geology and climate. To me, what gives an ecosystem its character is its plant life. The Everglades has quite the cast of characters, with grasses inhabiting the freshwater sloughs and marl and coastal prairies. Marl prairie is grassland of thin soil formed on top of limestone bedrock. The soil is high in calcite and the bedrock may be exposed in some areas. Rainwater becomes acidic as it dissolves plant material, and even a weak acid can easily dissolve limestone. The bedrock here is very porous. Marl prairies drain slowly.

Marl prairie (Florida Museum of Natural History)

Freshwater sloughs are main arteries for water flowing to the sea. The water moves very slowly and is very grassy. The sloughs are dotted with “islands” of trees and are bounded by the higher and drier marl prairies.

Freshwater slough (NPS)

Mangrove forests line the channels and rivers in the coastal and estuarine areas of the Everglades. Mangroves buffer the coast from storms, collect sediment to form new land, and harbor a vast array of birds, reptiles, mammals, and fishes. See my earlier blog post for more details.

Mangroves (NPS)

Hardwood hammocks are dense wooded areas on slight rises. Temperate and tropical tree species mingle here, and because the surrounding lowlands are either wet or not land at all, fire rarely reaches here. The dense canopy creates a dark and humid environment where ferns thrive.

Hardwood hammock (NPS)

Pine rocklands form on high ground around exposed limestone bedrock. These forests are less dense than hardwood hammocks. Fire keeps the understory open and hardwoods at bay.

Pine rockland (NPS)

Marine areas of Everglades National Park also have plant communities. Seagrasses stabilize the bottom, trap sediments, provide a nursery for fishes, and feed underwater herbivores. Lobsters, crabs, shrimp, corals, and sponges are also found offshore.

Florida Bay marine habitat (NPS)

Next week we'll look more at the plants and animals of the Everglades, as well as challenges the region faces. Information and photos this week come from the National Park Service.

The Good Old Days

This week’s adventure takes a peek at the past. Earth was a vastly different place in the good old days. Dinosaurs ruled and everything was just a bigger, sabre-toothed version of the critters we have today. OK, maybe not the bigger, pointier critters. But scientists can tell us a lot about the way things used to be by looking at the fossil record.

Fossils are like prehistoric pictures. They form when dead organic material is slowly replaced by mineral material. Not everything that ever died was destined to become a fossil; only in certain conditions could the transition take place. Being in a situation without oxygen would’ve helped your cause if you were hoping to fossilize. Oxygen is a requirement for decomposition. If you’re decomposing, you won’t leave behind anything to fossilize. 

Little worm fossils imprinted on a rock

Usually when you think of fossils you think of huge dinosaur bones. There are other types of fossils too. Footprints in dried mud that later turned to stone can be found in Alaska and Africa.

Dinosaur footprint found at Denali National Park (NPS)

Imprints of shells in rock are mountains that used to be sea floor. One wound up in my back yard in Pennsylvania. One day a dead plant was buried in between layers of sediment that hardened into rock. Years later, I squeezed that rock and found black images of that plant inside the rock. Whole trees can be fossilized into petrified wood. Ancient insects trapped in tree sap that hardened into amber are also fossils.

A rock full of shells from my back yard

Plant fossils inside a piece of sedimentary rock

If you want to find some fossils, you don’t need to be a paleontologist or geologist. All it takes is a little luck and some sedimentary rock. Igneous rock is volcanic in nature, so that won’t be likely to preserve any critters. Metamorphic rock is rock that has changed from heat and pressure, so no luck there either. But sedimentary rock is just dirt that compacted into rocks. If you go on a fossil hunt, respect private property and remember not to take anything from or do any damage to national parks.

Petrified wood- looking at the rough bark

Petrified wood- look closely and you can see the grains

Ant trapped in amber (Smithsonian)

Magnificent Mangroves

It’s common knowledge that trees are important. They provide oxygen, shade, habitat, food, and useful forest products. In tropical and subtropical areas, there is an important tree that is vanishing from coastal areas at an alarming rate- the mangrove.

Mangroves are annoying because they tend to live only at beaches that developers around the world want to develop. Mangroves are wonderful trees because in addition to the ecosystem functions they perform for nature, they also have ecosystem services for humans, if we would just leave them alone. They form a protective barrier against storm surges and trap sediments in their root systems, extending the coast outward as a buffer against sea level rise.

Mangrove forest (USFWS)

Mangrove species are able to tolerate brackish water. They have tall prop roots that keep the bulk of the tree above high tide. The root system slows water, allowing sediments to settle out. Eventually, enough sediment accumulates that the tree is on solid ground and new mangroves colonize the water in front. Small organisms like the safety that mangrove roots provide.

The tall prop roots are obvious at low tide (NOAA)

Mangroves are able to handle brackish water because they have a salt gland, so to speak. They excrete the salt through their leaves, bark, or roots. Some of the leaf excreters keep their leaves, which have a salty coating. Others accumulate salt in the leaf, and shed the leaf when it is saturated with salt. Those that excrete salt through their bark also use the shedding method to get rid of the salt.

Now that we’ve become aware of the mangroves’ benefits, we’re slowly making progress toward preserving the remaining forests. Here in the US, there are three mangrove species (red, black, and white) with a historic range being the Gulf coast and both of Florida’s coasts. Today, the best example of a mangrove forest can be in Florida at Everglades National Park. If you ever get to check out this important ecosystem, please do!

More great prop roots, this time on red mangroves (NPS)

This week's mangrove facts come from NOAA and American Museum of Natural History.