Unusual Ponds

– this another post from Bruce Bratton’s artfully produced BrattonOnline weekly.

Humans make ponds wherever we can. I bet you can think of half a dozen created ponds easily. Fountains, reflecting pools, “water features,” agricultural ponds, and cattle ponds are scattered across this landscape. Because of our innate affinity for water, we find these artificial ponds beautiful, and when we see the frogs, snakes or salamanders floating around them, we smile. If most of the ponds were created by people, here did those frogs come from, originally? Why are they here?

Natural ponds are odd anywhere, but especially unusual around this Mediterranean region. It makes sense that ponds fill with gradually with soil and muck and disappear with time; and yet, there are old natural ponds. Without human assistance, very specific circumstances must be aligned to create a divet in the earth large and big enough to hold water and qualify as a pond. Without people, something powerful has to occur to keep a pond deep and wet. The powerful and mysterious natural forces that create and maintain ponds have also helped to create a wealth of critters in natural ponds that have been roaming the landscape enjoying the more recent human-created ponds.

There are five natural types of ponds along the Central Coast: sag ponds, vernal pools, dune slack, oxbow, and cave ponds. Sag ponds are the majority of the region’s ponds and were created and are maintained by earthquake faults. Vernal pools sometimes get big enough to qualify as ponds and arte created and maintained by gophers. Dune slack ponds are a creation of waves rearranging sand. Oxbow ponds are a result of floods along streams and rivers. And, cave ponds are caused by the dissolution of limestone resulting in the creation of subterranean cavities.

Sag Ponds – Earthquakes

One of my geology mentors once told me that any natural pond I would encounter along the central coast of California would coincide with an earthquake fault. Interestingly, two faults, both named “Frijoles” have two of the best-known natural ponds of our area. The pond along the main trail for the elephant seal tour at Año Nuevo lies on one of the two Frijoles faults. As Kathy Haber pointed out, this has a dam and spillway that you traverse while on the trail. The T sheet from the late 1800’s shows a dark smudge that might suggest a wet depression, or pond, so “seminatural” or “augmented” pond might be a better description.

On the opposite side of the Bay, the pond in front of the big pink hotel in Sand City lies on the other Frijoles Fault. Less accessible to the public are the many natural ponds along the San Andreas fault above Watsonville. There used to be a large sag pond right under Highway 1 just north and adjacent to the Freedom Boulevard exit. And, there is another sag pond on private land in the northern part of the Swanton area. No doubt there are other sag ponds I haven’t listed…All of the ponds I listed above have water year-round.

Vernal Pools – Gophers

There are vernal pools in the mima mound habitats around the Monterey Bay. These include at Point Lobos, Fort Ord, Pogonip, UCSC, Moore Creek Preserve, and Wilder Ranch. Most recently, scientists have become fairly certain that those pools are a result of thousands of years of soil displacement by gophers. The soils excavated from the vernal pools are adjacent, forming what are called ‘mima mounds.’ Vernal pools are ephemeral, meaning that they do not hold water year-round.

Dune Slack – Waves

Behind and among the dunes that ring the Monterey Bay, you can find another type of ephemeral pond also called dune slack. These ponds are the result of surface water or shallow groundwater not being able to drain downhill due to the presence of natural sand dams, piled up by waves and wind.

Oxbows – Floods

The bigger streams and rivers carve channels during flood and sometimes then revert to another channel afterwards, abandoning an area carved deep enough to become a pond. Neary Lagoon is the best known one around here. There’s another that a prehistoric Carneros Creek carved down Elkhorn way. There were probably more near the region’s large rivers, but those are now farmed or paved so it is hard to tell.

Cave Ponds – Plants versus Rock

Very few people have seen the local underground cave ponds; most of them are inaccessible. Imagine clear quiet ponds surrounded by crystal-sparkling white limestone with occasional musical echoes of dripping water. These are tens to hundreds of feet underground from the San Lorenzo River around Felton to Scott Creek on the North Coast, with large caverns under UCSC, Wilder Ranch State Park, and Bonny Doon. Rotting plant leaves and needles leach humic acid that dissolves limestone, so caves and cave ponds are created by plants.

Pond Critters

Our region’s various types of ponds support a wealth of interesting pond-dependent indigenous wildlife including newts, salamanders, turtles, toads, frogs, and snakes. California and rough skinned newts are pond denizens, found naturally in especially in cooler, shadier sag ponds. Salamanders enjoy more sunny and warm sag and oxbow ponds, as well as vernal pools and dune slack. (Santa Cruz long-toed salamanders are critically endangered, despite valiant efforts to protect it) The California tiger salamander (less endangered but still rare), Western toads and rare California red-legged frogs also like warmer, sunnier ponds, which often host a cacophony of common Pacific chorus (tree) frogs.  One of the rarest pond creatures, evolving in sag ponds, is our only earthquake snake: the San Francisco garter snake; it is quite lovely and can be seen around Año Nuevo and north to the Bay.

All of these pond critters must have hundreds of acres of upland habitat surrounding a pond in order to thrive as adults. They mainly use the ponds as nurseries for their young. The upland habitat is where they find enough food as adults. 

Critter Food

There is enough food in ponds to raise baby critters, but little in cave ponds. Frog and toad tadpoles eat algae. Garter snakes and newts eat frog and toad tadpoles; garter snakes also eat newts. “Newts??!!” you might cry “but newts are super toxic!!” Garter snakes are constantly evolving to be immune to the constantly evolving newt toxins. Down below the ground, the slow-moving cave-dwelling and as yet unnamed potential subspecies of California giant salamander eats also very rare cave bugs and whatever other invertebrates might accidently wash underground.

The invertebrate community in ponds has its own food webs. Some of our favorite insects, dragon flies are one of the pond creatures at the top of the pond food chain. Before they grow wings, fierce underwater dragon fly larvae are like the tigers of the pond world, hunting anything they can grab and shred into bite-sized pieces. Lucky schoolchildren get to observe drop of pond water under a microscope and see zooplankton and lots of other teeny tiny things floating around in what might otherwise look like ‘clean’ clear water.

Back in People Ponds

It is not wrong to be inspired to create ponds, but we must be careful how we do that. Our people-made ponds can serve as new habitat for native critters, but if we add bullfrogs or fish, we’re setting up lethal traps and spreading bad things across the landscape. Non-native organisms will transform what might be a biodiverse pond into a much-simplified ecosystem with no salamanders and few frogs. More and more people are building raingarden (aka rainwater infiltration) ponds- these are more like vernal pools and rarely last long enough to support many pond organisms. Chorus frogs or toads might be able to hatch from eggs and grow past tadpole stage (“metamorphs”) in a raingarden pond that lasts three months.

It is quite a bit of work to keep longer-lasting created ponds full of water without concrete and with the addition of increasingly precious water. Livestock managers have become expert at creating and maintaining ponds, and now parks managers are learning from them how difficult and expensive that work can be. Because of the rarity of many pond organisms, that knowledge is precious but the viable partnerships/funding to do that work is a constant challenge.